Yes the heads were flat checked the cylinders that are dead are 4,7,and 8

OK this is my first time forgive me, I have a 1976 f100 custom single cab 2wd 302 c4. It has 3 cylinders with 0 compression the other 5 cylinders have 120 psi , I pulled the heads and checked the pistons, no holes in any of them cylinders were clean with no ring groove, I had the heads rebuilt...