You'd be time and monies ahead to get a v-8 car in the first place. That way you don't have to piece together things like a K-frame, motor mounts, wiring etc.

The v-8 cars usually have slighty thicker torsion bars, more leaves in the leaf springs, bigger brakes (often disc in the front) too.

Trust me, I took a /6 3 on the tree car and made it into a 440 BB with 727 auto!