compression ratio on pump gas

What Scamper is trying to do is have an engine like mine or Dave Clements. LA 360 with magnum heads. Dave and I both have 10.58 to 1 compression and can run 89 octane. I prefer to run 91 just to be on the safe side. Scamper is using the same cam and rear ratio as I am.
I gave him some advice on his piston choice. It was my opinion and it works for me. I also gave him some advice that I think was more important and that was to talk to Dave or moper about it.

I run KB107's that are zero decked with a .045 thick head gasket. My personal opinion is that he doesn't need the forged pistons he is looking at and a set of hyper's would work perfectly good at a fraction of the cost.

Seeing as he is having this engine put together at a shop and was planning to have the block zero decked then he should be o.k.

I was unsure what the lower compression would do to the combustion chamber shape. I thought it may change it enough that he would end up with a car that wouldn't run on pump gas. That is why he is asking the question here.

Jack