freshly rebuilt sbc will not start

[JP_67_GMC]

I have tried everything that I can possibly think of, along with several other people. Just rebuilt a 350 for a 72 Gmc, HEI distributor and an edelbrock carb that were used with great success. I have my timing on, I have firing order memorized. The Distributor is NOT 180 off. The rocker arms are not to tight, it is grounded to the frame. It has all 3 essentials but they refuse to work together. I do get a slight pop like one cylinder is firing when I play with the distributor but I can never hone it in to get it working. Also the cam in in correctly and I have brand new spark plugs and wires. I have moved the distributor around several times with no success, basically start fresh by taking everything off and starting over. Thanks