HY DIY.MechanicMike, My Euclid catalog only lists only two different kingpin possibilities for a 1972 C50 the 5000 lb. front axle GM p/n 3927942 which is Euclid p/n E-4444B Napa p/n NCP2621472 $76.49 online price. The 7000 lb. front axle GM p/n 3927943 Euclid p/n E-4443B Napa p/n NCP2621017010 $165.99, NCP2621473 $92.99, TWD HKP27.35 $69.99, TWD HKP2080 $76.49 those Napa p/ns represent at least two different product lines, but confirm that they will fit the axle you have, hope that helps.
