As I move toward an open drive line in my 54 with manual trans, I find many transmissions for sale that can be accurately evaluated only by the cast or stamped numbers. I have found the necessary decoder for engine numbers, but similar for transmissions are skewed toward automatics, and a search of this forum wasn't sufficient, and AI isn't as smart as it claims. The unit I am currently looking at has cast numbers GM4, GM H246, and 8889564. I believe it is a 1960s 4 speed, but have no more info than these numbers. Is there a comprehensive list of casting numbers for the several makes of GM transmissions?
