On a strict budget, one of the best things you might be able to do is find a later roller cam 318 in a pick and pull. They came in at 9.0-9.2:1, and have better flowing swirl port heads. Lots of ‘85+ M-bodies came with those motors. Add a stock 4bbl manifold and small carb, and upgrade the cam if you have any budget left over.
I found a roller 318 in an 88 Fifth Avenue for $200 with 80k miles on it. Lots of Ms came with ultra long rear gears, so those are usually very easy miles.
A 318 Magnum pullout makes an even better starting point, but requires a few extra tricks (and expenses) to make a clean swap.
With an early F-body, you’re going to have a tough time routing dual exhaust around the offset gas tank. Your best options are dumps/side exits by the axle (if you can stand the noise), or Y into a single 3” exhaust where your catalytic converter was. The single 3” is much easier to route, and performs just as well as 2.25” duals. You can run duals with both pipes going down the passenger side of the gas tank, but it will require a good exhaust shop to find the space.
