Any known history?

[PHAT69AMX]

If I may, if the ol' gray matter is workin' properly...

Holley List 4777 is a 650 CFM Double Pumper, progressive linkage, and has 4x 1-11/16" Dia. Butterflies.
Holley List 4776 is a 600 CFM Double Pumper, progressive linkage, and has 4x 1-9/16" Dia. Butterflies.

Holley List 4295 is a 570-585-600 CFM (depending on source) Double Pumper, 4x 1-9/16" Dia. Butterflies,
and was the '2nd Design' for the CrossRam, replacing the List 4210 being the '1st Design', Single Squirter, Mech Sec, 1:1 Linkage.

Note: Research suggest the Holley List 4295 ~600 CFM was the 1st ever Holley Double Pumper Carburetor,
most likely co-developed side-by-side with the List 4296 850 CFM Double Pumper, OEM on the '69 ZL1 427,
and also ~early 1968, the '2nd Design' released by GM for the L88 Corvettes.

The List 4776 is the only 'universal' Double pumper to have the smaller 4x 1-9/16' Dia. Butterflies.
All 4777 650 cfm through 4780 800 cfm carbs have 4x 1-11/16" Dia. 'Flies, & only the 4781 850 cfm has 4x 1-3/4" Dia.

The List 4776 CFM universal Double Pumper is dimensionally the same carb as the List 4295.
Differences: Fuel Bowl Inlets, 4295 inlets are 'Left Handed', Inlets are on the Bellcrank side, opposite inlet side from almost anything else, and should not be swapped Front to Back as the Float Level Site Screw Hole elevations are different for Primary than for Secondary,
and the Throttle Cable Bellcrank 'Style' is different on the 4776 but also Progressive like the 4295,
but the 4776 most likely will need 'trimmed' to clear the manifold clearance pockets.

The genuine GM 2x4 CrossRam Intake Manifold is the only one afaik that the 2 carbs
mount to it pointing different directions, the driver's side carb faces the firewall.

That may 'allow' a pair of good ol' List 1850 600 CFM Vacuum Secondary Carbs to 'work' on it.
And they could be retrofitted with Center Hung Dual Feed Bowls if so desired, like those from a 3310,
BUT the Secondary Float must be 'watched' since it must be one with a Shorter Float Arm so it does not
contact or rub against that 'hoakey' Secondary Jet Plate that's there rather than Metering Block & Jets.

If anyone knows the List 4295 and / or List 4210 Internal Specifics,
Idle & Main Air Bleed Diameters., PVCR Diameter(s)., and Idle Feed Restriction Diameters,
that would be welcomed information to have.

[z28z11]

There are several differences in the 4210A and 4295A 4150 Holleys, from jetting to bowls to metering plates and power valves. If you have the 34-1 4150 parts legend you can decipher the numbers a little easier. My scanner is down or I'd include one.

4776 carbs will work fine (use the early -1 or -2 gens) - there is an approximate .100" difference in the bowl level sight screws between primary and secondaries (for fuel shift), you can account for this when setting the float levels. Jets and power valves can be matched to 4295 (or 4210 if preferred), I'd replace the throttle blade with the Holley 20-3 progressive blade, which in function and appearance is pretty close to the 4295 original plate setup. 4295's also did not have a choke plate, air horn was not drilled for it. If you use an Offenhauser manifold, you need to add a little clearance to the rib under the leading carb's primary pump and pump arm to clear, or it will bind. Find someone with a good Bridgeport and remove the Offenhauser linkage tabs, and run the factory cable bracket, cable and 6 cylinder accelerator pedal. Reproduction everything else, and you're in business.
 
I'd run headers to improve overall flow if you're going to run one, much better flow than the standard exhaust manifolds. "140" off road cam can be used, a little stout for the street (and affects manifold pressure/vac on the power brake side). Small blocks have to breathe - that's a lot of mixture to stuff through even a great set of heads. Best to allow for the higher rpm application intentions, but it still looks great to see the setup at shows -

Regards,
Steve

[PHAT69AMX]

Only discussing, nothing more.
Ah, it appears the Offenhauser SBC Crossram also mounted the carbs in different directions.
Forgot to mention in previous post, the ambiguous List 1850 600 CFm Vac Sec
has 1-1/4" Dia Pri Venturi & 1-5/16" Dia Sec Venturi & 4x 1-9/16" 'Flies,
which are the same dimensions as the 4210, 4295, 4584, 4776, and others.

In scans of a 1971 Holley Listing, it shows same Jets and Power Valve for 4210 &  4295?
#69 Primary, #6.5 Power valve, #71 Secondary.
If only had the Air Bleed, PVCR, & IFR sizes from a 4210 & 4295, which unaware are in any chart.
If someone who has those in-hand would measure them with pin gauges that would be awesome, invaluable.

The 20-3 Throttle Shaft & Bellcrank Kit, Cam Follower in Slot Type, appears to be 1:1 rather than Progressive.
20-3 a service replacement for the List 4224 660 Center Squirter, so shaft flats are for 1-11/16" Dia 'Flies,
where the 4210, 4295, 4776 have 1-9/16" Dia 'Flies, so do the too wide shaft flats matter ?
4210 was 1:1 Follower/Slot, a fixed radius slot, 4295 was Progressive Follower/Slot, a 'W' shaped slot.
Holley used to offer a 20-27 Throttle Shaft & Bellcrank Progressive Kit with the 'W' Slot like the 4295.

Wonder if Braswells or Holley or someone might sell just the Throttle Shaft Bellcrank end pieces?
Then a person could just swap Throttle Shaft end pieces on what they have, like if starting with a 4776.
And agree, start with an early -1 or -2 4776, but man newer QF or other versions have some
nice additional features like bowl site glasses,  screw-in air bleeds, maybe even changeable PCVR's.

In a conversation with a retired GM Engineer, he laughed about the 4210 4295 left handed inlet fuel bowls.
Intent was factory set-up with everything in between the 2 carbs for 'neat packaging'.
But in practice and racing it was very impractical, so racers swapped the Bowls Front to back,
resulting in both carbs having outboard fuel bowl inlets, and the engineer said he had a 'process'
to compensate Needle Adjustments due to the site screw difference, as you mentioned.

[z28z11]

Me three - just a discussion.

Carbs mount the same between the factory Winters casting and the Offy. Throttle linkage reliefs are dead close, too. Basic cosmetic differences are the top plate bolts (1/4" Offy, 5/16" Winters), the raised rib around the periphery of the top plate (slightly more substantial on the Winters, slightly inset more). Internally, the raised flow directionals are close, again more dramatic on the original. All of the reproduction gas lines and cable mounts bolt right up with no mods. You have to machine down the notch for the accelerator pump on the passenger side carb to allow the carb to sit flat (and the pump to operate), which you can do when machining the Offy linkage bosses (and the logo if you'd like) off the top plate.

I chose the 20-3 in the past as an available part from Holley, close enough to appearance and function to work. I don't see the other number you mentioned as being available (maybe used or eBay ?).

I started modifying the Offys several years before the reproduction setups came out - I always thought I would build one for my X77 car, but had second thoughts about originality and decided to keep my 4053 intact. I ended up building 4 Offy cross rams, sold them all along with most of my accumulated cross ram parts, with a few exceptions of a few very rare ones. I still may convert one of the Z's some day, but it's not high on my priority list. I must have gotten pretty close, no complaints or returns on what I sold. If you added the original casting numbers; they pass for Winters at a glance, but I would not want to violate copyright laws by doing so.

Why did I go to all this effort ? Pretty simple - HBC sold an NOS setup years ago in the $20K range, people were selling Winters bare intakes for $5-10K, and then the repros came out at $4K+ for the bare intake, about $8K filled out. I put a whole let less money into mine, and charged accordingly to what I had in them when I sold them.

Sorry to hijack the thread -

Regards,
Steve

[PHAT69AMX]

L78 Steve, the original poster, was looking for input, was he not, about what carburetors to use with a CrossRam, and the last few post, would imagine, would give him quite a bit to contemplate.