if they are dished, 64cc heads should be fine for compression. you will be under 10.5:1 depending on head gasket thickness. Or if you intend on hitting it with any sort of boost. Two pistons that hit the floor, well, stress cracks will disinegrate the piston inside the block when you run it....get them magnefluxed to be on the safe side. Even though you were not intending to use the pistons in the beginning, it is always a wise choice to carefully take out the old parts and inspect them carefully to see how well the machine work was originally done....any scuffing etc. this is a good practice to see how good of a core you are going to be working with.