whenever possible, we sell and use new cast pistons that don't have this problem, but for certain cubic inch nailheads, this is potentially an issue no matter what cast piston brand you obtain for your engine, and regardless of decking the block and surfacing the heads.
shown below is the most common place, the piston will hit the head. take note that this is not the ONLY place i've seen them hit. the more rare area of contact is ABOVE the valve relief notches on the area on side of piston towards the lifter gallery. the more common place with certain perticular brands, are the dome corners opposite of the valve reliefs, shown below, outlined with a black sharpie. that area needs the edges beveled/ rounded, otherwise they can potentially hit. nothing worse than getting your fresh built engine stabbed in the car and then find out the whole thing has to be torn back down because the pistons hit the heads. remember that you need .035 absolute minimum on a street engine, between all areas of the piston and the cylinder head. this can be determined with play doh/ clay and crushed head gasket thickness specs.
i round the edges with a 2 inch rolox sanding pad to do an even and quick job of it. you can file it by hand, but odds of slipping and damaging the piston are greater that way, i've found. remember to do this before balancing of the pistons and pressing the wrist pins. (pistons should be thoroughly washed afterwards) sanding and grinding obviously creates a lot of contamination. always balance the pistons and rotating assembly on these engines when you build them. the added expense is cheap in the grand scheme of the money you will have invested when you are done.
