I ordered the slip yoke for the rear of the transmission. Put it in and bottomed it out, measured from center u-joint to center. Took that measurement and the slip yoke to the driveshaft shop and told them what I had and what I needed. They took the measurements and made a drive shaft. I think there was about an 1 1/2" slip on the front yoke when installed. It cost me a little over $100 at that time and it sure beat trying to find something that would fit.

51 GMC 100 with 59 chevy 261 under the hood.
3 on the floor with 3.42 gear.