how much hp you can get depends on how much money you have, as well as what your intentions are for the truck .... the more highly modified the engine is the more time you'll spend keeping it 'just so' instead of just driving it - a 283 blueprinted to the 195hp version can collect lots of traffic tickets without much fuss keeping it running well, and they sound a treat with the right exhaust system

a healthy 283 can do a lot of towing with the stock 3.90 rear, and an OD 3 speed will help on the highway
Bill