Kool thank youNope, you can't.
350 Chevy is 4.000" bore(with 3.48" stroke)
Pontiac 350 is 3.875" bore(with 3.75" stroke)....the Pontiac block will not take a 1/8" overbore, you will hit water.
2nd problem would be they have different piston pin diameters.
3rd problem would be they won't have the valve relief clearance notches in the right location to match the different valve angles and locations.
4th problem would be the istons are different height...even if you could manage to get around those first three problems, the Chevy piston would sit more than 1/8" lower in the bore at TDC....compression ratio would drop below 7:1
Only 350 Pontiac pistons are going to fit a 350 Pontiac....or aftermarket stroker pistons and a 4.21" stroke crank to make a 402" stroker out of it. May also be a 4.0" stroker crank, to make a 382" engine out of a 350 Pontiac.