I'll know for sure in about two months, because I'll be changing in a 4-speed for the 3-speed in my Suburban.
I also gave up on the three speed because I did not want to keep playing with the shifter box, the linkage rods, and the shifter forks and the spring and ball detents inside the transmission. Also, the first gear in the stock 3-speed seemed a little high for the 3.55 ring/pinion conversion.
The last 1/2 ton 4-speed u-joint assembly that I used was a NOS unit that came with the correct yokes. However, it is my understanding that if you use the 4-speed-side yoke from an enclosed driveshaft transmission and the 3-speed yoke from the enclosed drive-shaft end, and a 3-speed/3-speed joint/cross, you'll be OK.
Be sure to follow the Shop Manual procedure for determining the correct number of gaskets between the ball/bell collar and the transmission.
