Stock 72 318 power gains

I would use this camshaft and advance it 4 degrees COMP Cams 20-221-3 COMP Cams Xtreme Energy Camshafts | Summit Racing dont waste your time porting the exhaust manifolds, just port the heads, and run dakota 2 1/8 exhaust manifolds or if you have power steering run a 73 340 driver side manifold.

With compression it will be hard to get it to decent ratio with out changing pistons my 72 block was measured at 7:8:1 with stock heads and pistons. I milled 302 heads down to 58cc using 1008 felpro gaskets and barely got a 8:1 range. In your case i would put more effort in the heads and valve springs and advancing the camshaft