Guys, FWIW, Below is a screenshot taken form the
1956 Chevy Truck Data PDF that specifies the standard transmission speedometer gear set teeth counts and a list of the various ratio adapters. Someone can do the math to figure out which of the listed ratio adapters would provide the closest correction for Mickey's 3.07 current axle ratio. Also attached is a picture of a little later NOS 7-20 speedometer drive set so you can see what it's supposed to look like.
