Edit 8/20: This is from a discussion that was in the Project Journals: 1927 Chevrolet Capitol 1-ton -- Full frame-off resto. If you want to see any of it. (The *you* in these posts is John. 
) As I'm going through Lurch's clutch area, I noticed something that would be useful for you (John M.) to check out on your 1927 truck build.
In 2017 when I rebuilt Lurch's engine, I also switched over from the 1927 worn out 3-speed transmission to a refurbished 1928 4-speed.
The 4-speed had the front yoke of the u-joint already on it and I just bolted it to the 1927 rear yoke that was already on Lurch's drive shaft. Now that I've taken this u-joint out of my truck, I've learned that the '28 trunnions (the donut u-joint bearings) are larger in diameter than the '27 trunnions. That made the rear yoke loose as a goose and caused a lot of scraping and scoring inside the u-joint ball housing.
Sooooooooo, since you've got parts from multiple trucks, some '27, some '28, and who knows what, I strongly suggest the u-joint that you put together has has a matched set of the larger trunnions and that they fit well.
I don't know what the clearance specs are for the tunnions on the yoke shafts, but if you have a bunch of parts, use the ones that show the least wear.
Update: I realized that I have a NOS u-joint assembly for a '25-'29 Chevy car in my stash of parts, so I disassembled it and measured the gap between a trunnion bearing ID and the shaft that it runs on OD. The difference in diameters is .004 inch. ;-)
Also make sure that when you assemble the u-joint, face the side of the trunnions with the bevel towards the center of the u-joint.
Ever onward, Dean
