I don't believe the threaded shackle pins and bushings are a common size or thread profile.

The good news is the bushings press out of the brackets in the frame (and spring eyes) and new bushings with pins come in the replacement shackle kits.
Picture and part numbers here and following pages
http://chevy.oldcarmanualproject.com/parts/1929_54/432.htm

New parts can usually be had at NAPA or other auto parts stores, spring shops, or the usual restoration parts suppliers.

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-