New engine, won't run!

[brothers69c-10]

I finally got around to installing the big block in my 78, but can't get the darn thing to run. It is a completely rebuilt 427 tall deck motor. I have checked the distributor 5 times to make sure it is on top dead center of the compression stroke. Put in different plugs, new fuel pump, different plug wires, different cap and coil which i know is good. Adjusted the distributor every which way, Tried setting a tooth off in either direction. Cam was installed properly. Double checked valve clearances. I am out of ideas. It turns over fine and it will pop and sputter, no backfiring, but it will not run. I am out of ideas.

It's getting spark compression, and gas, and i am darn sure its in time. I have had a darn good mecahinc of 30+ years helping me and he can't figure it out either.

Any advice would be appreciated.