Jeff, NOBODY is shooting down your car.....
The known facts, so far, are that it appears to be an early build L30/M20. There was NO 325hp 327 in a 67 Camaro. The 325 hp rating was for a L34/396. If the small block engine you have is indeed the original, that eliminates a big block car. If the aluminum Muncie transmission that you are going to look at has the matching VIN to your car, then it very well could be a big block car and the small block you have can't be the original UNLESS the engine is a 302. The car very well may have come with a factory 10 bolt axle, as you point out, and it then wouldn't have a radius rod either. You are correct on that point. The fact that is has the stiffener plate under the rear seat for the rod, indicates that it is from the mid-year, transitional period, where GM was attempting to address the severe wheel hop in the higher hp, manual trans cars. I know you are excited and are still hoping you have a 1 off, super rare car, but the odds of that are pretty remote.
The reason GM stamped the VIN in the 350's was because it was considered a high performance engine and at greater risk of theft than the 275 hp 327. The 327 had been around for a number of years and the 350 was brand, spankin' new in the 67 Camaro ONLY.
The M20 designation for the transmission in the tt decoder was for ANY 4 speed equipped car. It is confusing because Muncie used that designation for one of their transmissions. M20 behind a 327 would've been a Saginaw brand, cast iron case, transmission. That will be the first thing to look for when you view the "original" trans that he has. A lot of people don't know the difference between a Saginaw, Muncie or Borg-Warner 4 speed trans and the owner may be mistaken as to what it really is.
By the way......my 67 was built about 1200 after yours. Build date 2C and is from Los Angeles too......
My car does have an original 12 bolt axle with the bracket provision for the rod, but no evidence of one ever being installed due to the transmission being an automatic and not as prone to the wheel hop issue.
Hang in there, man. It's still exciting and I'm very interested in what you have yet to discover, as are probably others...