Cylinder Head Choice

With a 2.76 axle, 318 cubes & the small cam, you might actually go slower with alum heads. Not a recipe for performance. Because you are putting performance heads on a non-performance engine.
From what you have said, only mod is this very mild cam.
In my opinion, with what you have said, better performance will likely be realised by having a multiangle valve job, with mild clean up in the valve bowl area of the factory heads.