73 and up 4x4 12 bolt in a 72 and earlier?

[Fast68Chevy]

73-up 1/2 and 3/4 ton 2wd and 3/4 ton are 42.5" spring pad spacing and so are 2wd 1/2 and 3/4 ton 64-72 except for longhorns

only difference is one shock mount which is easily modified, get tape measure out to measure to make sure on dimensions

70-72 axles are wider than 73-up light duty 1/2 ton axles by about 3/4"
57" plate to plate in 70-72 and about 56 1/4" in 73-up
good luck