Runs only with valve cover pan unbolted?

So we finally got the timing set right on the old truck, dad had undone the valve cover pan to make sure both rockers were loose verifying that it was at TDC. He started it up and it was running good! However, i look over and smoke is billowing out from under the hood! He had left the valve cover undone and oil was spewing onto the header. So we tighten the valve cover back down, and it hasn't started since... any help would be greatly appreciated.

Pull the PCV valve out of the valve cover and try again.
You didn't pinch the fuel line did ya?

No, I installed neww lines and fuel pump.

There are different styles of fuel pumps, so make sure that the three lines are on the correct tubes of the fuel pump.

Most likely related to what was just "done".