Put a carb on it and try it. You can pull the fuse from the in tank pump and just fill the bowls manually. It will run on the bowl long enough for diagnostics. I’m betting this is a balance issue with stock crank/rods and lighter KB pistons.
I can see if I can track down a carb. How does the distributor react being locked out? So the weights and springs have been removed, so the efi can control the timing