Billy,
One thing up front, you really, really want an OD automatic for the car so it will be a reasonable highway cruiser. What would be really cool would be to latch onto a Buick Nailhead engine for it, and if that's out of the question then a takeout engine/tranny package from one of the LS machines. That said I understand that going basic 350 Chevy may be cheaper for you. I'm just a big fan of Ford in Ford, Chrysler/Dodge/Plymouth in their models, Buick in Buick, etc and I know I'm not alone. Later on a nailhead in the old girl will make her more interesting to buyers if you can score one. Check out Ahwooga.com Buy and Sell Automotive Parts and you might get lucky.