Ok, what are you calling pumo gas? Do you know the RON and the MON or at least the advertised Octane numbers of what you are wanting to run?
What is the principle and secondary application for this engine? Is it race only? Street drivable and race?
Do you know what your current valve to piston clearance is with current setup?
If your piston is in the hole .020 and your gasket is .040? .042? Then for your bore size you do not have much squish ability built in. If anything you may be having some pre-ignition and minor detonation problems if you are driving it on the street at low rpm part throttle operation.
If your valve to piston clearance can stand it, put in a thinner head gasket. Be certain just what your piston in the hole deck ht is first. Then you can safely shoot for a minimum squish/quench distance of .040 as long as you have enough valve to piston clearance. Yes' it will bring your compression ratio up but at the same time should give you a better burn pattern with a more efficient combustion fire chamber. (My term which includes cylinder head and piston all together at TDC.) That engine needs to benefit from the squish of air/fuel mixture that is only possible when the piston is near the cylinder head.
I disagree completely with the info of you only being able to run 10.00 -1 compression with pump gas. My 10.00 -1 street engines work great with 89 octane pump gas and my 10.00 -1 SB engines work great with 87 octane. My Steel head daily driven bb HEVYS AND mOPARS WORK VERY WELL AT 10.75 -1 COMPRESSION AND WITH ALUMIUM HEADS WE BUMP IT UP ANOTHER 1/4. and at times, slightly more. (Sorry about caps lock).
I am not telling you to run out and make your BB Chevy 11.00 -1 and higher just becuase I have good results though. Too many have tried and have burned up their stuff. To run high compression with station available pump gass it does take a little planning and a little extra work on the part of the engine builder. I have street/strip SB Chevys running as much as 11.30 -1 compression and they drive them on 92 octane pump gas.
You can do it if you do things right. I see no reason at all that with your cam specs, if you have a good quench/squish clearanced set-up, You shouldn't be able to run it above 10.50 - 1 and even up to 11.00 -1 if you watch and be careful in the assembly and get no more than a .045 quench/squish in it, with carefully sanding down by hand any sharp and rough edges on the piston, around the valve notches etc.
I am now in the beginning process of building a barn burner that will be capable of running on the street at 12.00 -1 measured static copression but will be using an av gas mix with other gas.
So do you need any different pistons to get more compression? I think you don't. Now' if you want to go further and make more power with what you already have and are buying new pistons, here is my suggestion. Buy them from me. lol. No' seriously I do some tricks in design and in dome shapes that if you will angle mill your heads to reduce the chamber size, we can get you more power even at the same compression ratio, but will use a small dome, flat top or even a reversed dome if needed and you will need less total ignition timing becuse it will be a more efficient design. Oh' I was sorta joking about buying them from me. If you call to BRC Performance you can still get my dome by asking for the EW Dome profile. If you need a dome. If not then we will need to design whatever it is you need to make it work like you want.
Still I think you can do just fine without buying new pistons.
Ed