Would the 3 speed overdrive from a 69 GMC be a SM326? If so, is it the same as the one for Chevy?
Yes, 1966 and later overdrives were SM 326 w/sychro first. GMC and Chevy should interchange. What year are you planning to put the 1969 transmission in? The SM326 likely has a larger bearing retainer on the front and finer spline on the tail from earlier non synchro (pre 1966) transmissions.
The casting number on the tailshaft is R10Q and the side cover has seven bolts. The early ones were R10H with 4 bolts on the side cover and non synchro first.
Here is some free reading material:
http://speedprint.com/deves50/overdriveindex.phpRegards,
Steve
New Orleans
