If you want to retain the original column shift linkage, then you will want to look for a three-speed Saginaw transmission with overdrive, used in Chevrolets from 1966-1970. Be sure that you get the solenoid with the overdrive, since that solenoid is unique, and those that fit other overdrives do not fit the Saginaw.
God's Peace to you.
d
Inliner #1450
