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Chevy's Dist. rotate clockwise, so buy turning the dist CC. you were advancing the timing further.
I have a buddy that can't get this right either, so now he takes the valve cover off & watches for both valves to be closed, then lines up the pointer at 0*
It's not necessary to change the dist location, you can just change the location of the wires, after you have #1 at TDC wherever the rotor is pointing, make that tower the #1 plug wires new home.
Plug gaps, fool around a little with the gaps, you may find a closer setting may work better for you
You can change seals while the heads are still on