As you already know the Paxton Novi GSS supercharger is a ball drive unit and 7 lbs of boost is a good limit for it.
Even though that is low boost, if you want a good safety margin I still would recommend a forged 2618 alloy piston.
We use Diamond pistons for racing applications.
The least expensive 2618 alloy pistons is Racetec.
In any case it will be a custom piston.
The pistons can be made with an accumulator groove between the top and second piston ring to prevent ring flutter. That is usually standard for Racetec.
If so then use BWE piston rings with a ZG second ring. There will be a lot less blowby under boost.
I picked up 2 inches of crankcase vacuum with a ZG second ring in our blown alky engine.
Bruce Walker at BWE will help you with ring selection.
This is a forged 4032 alloy Autotec piston for the 1965-1968 .912" pin 240 rod on a 300 crank with the accumulator groove.
It has a 10cc dish for a 9.75 compression ratio in a naturally aspirated 300 six
https://dl.dropboxusercontent.com/u/393 ... C01572.JPG
You will need to know the piston ring dimensions before you can order pistons.
I noticed you are using a large mechanical lifter cam.
Is this engine for street/strip?