i don't really have an answer for pretty much all your questions cause i don't have a clue with all them letters and numbers but my guess if you trans is a 4 speed that its a SM420 was told that 1967 and earlier 4 speeds were the SM420 and 1968 and after 4 spees were SM465

Nate

Link to my photobucket for pics of my vehicles
http://s238.photobucket.com/albums/ff17/OldIronChevy/