When I got my 76 F250 4x4 the 429 was already in the truck, kind of. It was a hack job with turn buckels holding from exhaust manifold to the frame. And the engine pertches on the frame had been cut out where the mount bolted to them.

We drilled and fitted 390 mounts to the 429 block. Then cut the face off off the engine pertches and refaced them using steel from a leaf spring. Lowered the 429 and the trans. into the truck and marked where the new mounts would set. Lifted the engine out and put the pertchs back out and cut new slots for the mounting studs. then reintalled the engine and trans. Total cost was less than $20.