If its a tight budget then a stock cast piston re-build kit, a good job on the heads (3 angle valve job, maybe clean up the bowls) by a good local shop or Muscle Motors or Hughes and a small Summit cam. If you're going to hot rod it I'd go right to a 440 crank and make it a 451. Its hard to get much compression or performance out of the 400.

A steel 440 crank can be re-ground with 400 mains or 440 source sells reasonably priced kits with pistons. Along with the cubes a little bigger cam like the "big" summit version would work well with mildly worked stock heads and 9:1 or a little more compression.