[camarojoe]

FYI, there are many different ratios on those adapters too, which throws yet another wrench into things... They were made by Stewart Warner, but factory installed ones also carried a GM part # too. The 4 speed Deuces used these. (4:10 rear ratio, M21 muncie)

The Yenko Deuce service parts catalog lists 2 numbers for the speedometer adapter. 6477965 and 6477964. I believe these are the GM part numbers, but SW also sold these with their own part numbers, with the ratio stamped on the end of them...I think the GM issued ones have the ratio stamped on the end as well...but offhand, i do not know what the correct adapter ratio should be. For as many cars as used these, its hard to find anyone who really knows much about them. I was told that they were required because there was not a plastic tranny gear that would work with a rear end ratio of 4:10 or numerically higher... but i just read above that some cars didn't use them depending on the trans, so if thats true, that disproves what i was told.