750 horse out of a 300. Really small horses I'd bet.

The 250 shares the same bell as the 240/300. The 200 is different.

150-200 horse is where you start with a 302. Getting 200+ out of a 300 is a bit of work, but not impossible.

FWIW, having had both a 300 and a couple 289s (and a smog motor 302), I'd go with a 302, maybe even a 331 stroker if I found some loot.

ymmv.