Truck will start but won't keep running!

[CSchmidt]

Hi everyone Chris here,

I have a 1967 chevy C20 pickup truck with a SBC 350 1985 engine. Had a oil leak and took the engine out and replaced all of the gaskets and new timing chain, 4 row radiator with dual fans, new water pump, new alternator, new ignition switch and spark plug wires the whole nine yards. Put everything back together and had some issues but nothing to bad. Was driving around for about 2 weeks and noticed the low drop in volts when I tried to start it well below 9-11 volts. I have a new wire harness to be put in but the biggest problem is that the truck will crank over but the volts drop after that. It won't stay running and if it does start and I drive it it will die and can't start it back up. Electric fuel pump works good but think it might be my distributor but dont know for sure. I have a video of the volts dropping but can't get it uploaded.

I would appreciate any advice and help to get my truck back on the road.

Thanks for your time
Chris