Thank you for your additional advice. I am confident that my problem was caused by that one pin rotating only one way as the spring worked back and forth. I had the bolts double nutted, so I do not believe that the nut backed off. I also do not believe that the bolt broke. The pins of the right side shackle assembly have not moved. I check it frequently, and the left side is holding at its having moved 1/32 inch since I fixed it. For now I'll keep checking and go with what I have if it holds where it is.
Again, thanks!
1950 GMC 100 Panel Truck, 1958 270, 3-spd Saginaw with BW OD, 3.73 12 Bolt Differential from a 1966 C10, Front Disc Brakes Bought it in pieces 9-1976, driving since 6-1978 Follow in the DITY | 
