[AZKen]

Trying to fit 55-59 Chevy Truck Upper front Shock mounts to replace broken 4X4 mounts. Had these salvaged from a project. Not sure yet. The removal of rivet method might be useful. Grind rivet head down flat. You will see the shank and see where center is. Center punch, drill about 1/4 + Diameter hole x 1/4 + deep then knock em out. Last pic, sizing up the donor to see if feasible. I say yes with some mod and new holes. Unless a better idea comes along.
P.S. The original 4X4 upper mounts seem have a breakage problem. The top is hanging out in the air. Unsupported where the stress is located. As you can see, the donor does the same. I will be adding a piece of angle or a "gusset" on top. Bolted to top frame flange and, I guess, welded to the mount. This will give the needed strength. I'll post when design is finalized.