Procrastinator,
The best engine to start with would be a small block 302 or 351 UNSTROKED. It's a little harder to find a 351 in the junkyard to rebuild but it should be worth it. Most 302/351 parts interchange so upgrades would be easy to get around 500 HP at some time in the future. The worst engine to use would be the 390. What a dog! Most can't outrun a good 250 hp 327 Chevy and parts are not easy or cheap! You asked!
h dog