If the heads are factory, they should be closed chamber 516 heads, and the Sealed Power 238P Pistons should work. I didn't have any luck through anyone but Summit, and the .040 over Pistons I ordered are not shipping out until 4/26. Good luck! Here is a link
http://www.summitracing.com/parts/SLP-W238P40/
Compression calculator is on this link. Pistons are .085 deck clearance with the 2.000 compression height, have your heads cc'd and you're on your way.