I've owned a 1979 Pontiac Trans Am that was built at the Van Nuys Plant since 1986 and have all the original documents for the vehicle, which include the window sticker, dealer invoice, warranties and maintenance invoices, and can say that although the VIN number is stamped on the Borg Warner Super T-10 transmission, the block was never stamped. For the 1979 model year, Pontiac shipped completed 400 cu inch engines to Van Nuys in 1978 and the engines were stored in an area next to the Cushion Room by the train tracks. You could identify the Pontiac 400 engines as they had chrome valve covers. The 400 engines for 1979 had an engine identification code of "PWH" instead of code "WC" that was used in 1978 for the Firebirds with 4-speed transmissions. Although I believe that the engine in my Trans Am is the original motor and has never been rebuilt, even though I was an employee at the plant when the car was built, I can't say what happened with my car as I wasn't the operator stamping the VIN numbers.
I also own a 1970 BOSS 302 Mustang and the last VIN number stamped on the transmission should be a "7," but shows a "2." The VIN numbers were stamped individually on the block and transmission in 1970 at the Dearborn Plant and I would find it difficult to believe that the transmission isn't the original, but I would only be speculating.
I will say that we didn't have air conditioning on the assembly line at Van Nuys when I worked there and during the summer, it got so hot, especially on the second floor where we used water-based paint. Not an easy place to work, but in general, everyone did the best we could as few wanted to be transferred to another location if the plant was closed.
