Riddle me this, Batman!

So you verified that #1 piston was at TDC on the damper and timing cover, (there are a variety of them) before you put the heads on? Assumed that you have a clamp-on induction timing triggered light? If it runs great, then must have the clamp-on the wrong wire. Doesn't run great, then the timing is off far enough to not show, likely ignition retarded, or cam to crank timing chain off.