[Stocker]

HO72 was typically on one-ton trucks... unless yours has been changed it is an HO52. Leaf springs don't matter afaik..... all K20s came with leaf springs. Cover gasket will be the same either way. HO72 has bigger brakes and possibly some bearings (axle bearings?) are bigger than HO52, but for the most part they are identical including the center section.