What’s the best new high hp motor that will fit in a 72 Scamp?

If your Scamp is set up for a small block, a 408/415 will get close to 500 horse without too much work. You will need a converter, a juiced up 904 (or 727 if you choose but not necessary) and a stout 8 3/4 rear with some good gears. (3:55 or better) Be prepared to boil the hides at will. It will be a handful to drive.