273 swap to 318/ build, cost, potential, daily driver

The deal breaker for me is the expensive intake manifold needed for the Magnum engines. Your car uses a complex kickdown system that would have to be addressed. If the car is a factory air car-some of the compressor mounting points won't be there on that new intake. The electric fuel pump, the cracked heads. I'd say, watch for a roller cam 86-91 318. The Fifth Avenues were generally well taken care of. Might be able to find a good one? I have to much LA stuff to switch over.