I have a 1969 Skylark custom 350/4, I installed the drive shaft and the nuts on the u-joint bolts are even with the end of the strap threads, not enough space to install the lock washer. I've purchase three different u-joint bolts however, they are all the same size. The last set was Moog #329-10. It fits in great however, it doesn't seem to be long enough either. The cup of the universal joints are 1 1/8", I also measured the differential flange and got 3 5/8" width & 1" tall. Any recommendations
Check to see that the u-joint cups are set fully into the differential flange pockets, if they are fully seated in the pockets, I would use the extra strong Locktite thread locker.
This is the way parts are being made. YOUR going to have tio keep trying different brands and hope someone gets it right. I personally have run across short u-bolts all the time. It should be fine with tock tight as long as the thread is level with the back side of the nuts you will be fine.