Ive read that the compression ratio should be less than 10:1 to run on pump gas. I wanted to error on the safe side, so I was thinking about 9:1 to 9.5:1. Of course, in 1972, the 340 CR was reduced to 8.5:1. Maybe that is the way to go.
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.
I agree with the guys above ^^^^^^^^^^^^as far as compression and a pump gas friendly stock cruiser/driver.
I'm curious as to the cam inquiry? The 340 replacement is fine for a regulation driver, even with 8.5/9.0 compression. I have to wonder if increased performance isn't really in the back of your mind? With the 4spd & 3.55's, there's no reason that the XE262 wouldn't be a suitable option. My personal opinion is, if you were willing to upgrade the carb, the XE268 would be right in my wheelhouse with that setup, regardless of the stock manifold's......Plus it still works with the single valve springs :D.
It really depends on how mild, or how hot, you want it to come out.