I don't think you're ever going to find a "hard" date for when the 4295 replaced the 4210 carb but it would have been sometime during the summer months of '68.
I don't have a collection of photos showing 4210 and 4295 choke tower numbers so I personally can't help with that but maybe someone else here can. Some of the pictures above show numbers altered with an electric engraver. I would not call that etched, and there is no telling who altered those numbers. Maybe I'm wrong but that does not seem like something Holley would have done.
You are correct that there is an error with the '68 cross ram carb listing for '68 on our carburetor page and I will get that fixed when an opportunity presents itself. The 3810 is thought to have been a developmental carburetor while the manifold was undergoing initial development. There would not have been a cross ram unit that left GM for public consumption with a pair of these 3810 carbs on it, in my opinion.
The '68 cross ram carbs should read...
302/290 (2X4) 3941140 (early) Holley # 4210
302/290 (2X4) 3957859 (later) Holley # 4295
You're also right about the 3942595 part number being incorrectly types for the carburetor when it was one of the fuel pipes so that is another thing for me to fix. I appreciate your help so that I can put correct information out there.
I don't believe the 4295 is the first Holley double pumper as I remember talking with GM engineer Bill Howell (part of Vince Piggins' Product Promotion Group) and he told me years ago that he was testing an 800 double pumper carb on the Penske Camaro right after the '67 Trans-Am season finished. This was before the cross ram was available and was in the Oct-Nov 1967 timeframe. I just asked him again a couple of days ago about cross ram carburetors and double pumpers and here is his reply..."As a test engineer in the lab, I had no release responsibilities, so I did not keep track of part numbers and minor differences in many new parts being considered for release. By the time the 2x4 package was released for production, I was in Vince's group, so I had limited interest in those details. I knew the carbs were 600 cfm, and their double pumper characteristics. In their production layout, they were difficult to work with, so we reversed end for end the float bowls to get the fuel fittings outboard. This also increased the difficulty in setting the fuel levels, as in production, they were different front to rear. I would have to adjust the fuel to the bottom of the sight plug, and then raise or lower it to the correct recommended level after reinstalling the sight plugs. Your recollection that the Marlboro test in 1967 probably involved a double pumper 800 cfm is correct in my memory (tho I have no written record for reference). It amazes me how accurate my memory of the 1960's is compared to the 1980's. I guess that speaks to the level of excitement I was experiencing during those times. I hope the above information is of benefit for your research."
