360 timing issues

You’re right something did change. That’s what I’m try to figure out. The only thing done to the heads was clean the old gaskets off and check for straightness. Pistons are all right side up in the same hole they came out of with rings at 10 and 2, and oil rings at 8 and 4 with center spacer at 6. I’m not reading where timing should be is the problem, and it won’t run where it should be.
You don't have 1 and 6 plug wires crossed, do you ?