Suggestions for the Best Comp Ratio, Pistons & Cam for Street 340

No more than a 9.5-1 with an iron head and a small cam.
IMO, a 9.0-1 and the MP upgraded 340 cam is a good choice. It's a step larger than the Comp cam with street manors.
Hyperutecic's pistons are fine and available in more ratios than a cast slug which comes as a OE replacement piston. You can do better than a
8.0-1.