Cranks and wont start ongoing issue

Looking for a little insight on a ignition issue that has me stumped. About a year plus ago I removed my Fast EFI and Mallory Hyfire 6 and went back to carb and to the regular hook up of the distributor (Mallory Unilite) through the ballast. When I hooked it up it almost started then would only crank (no spark). I re-hooked the Hyfire still no start and went through the troubleshooting for it and I have spark but no start (Unilite module bad). I replaced the module,(removed the Hyfire) reconnected back to ballast tried to start, it gave a almost start then just cranked, fried another module. "Definition of insanity". Installed another module, hooked it up to the Hyfire and life is good car runs. I do know that when then the unit is hooked up without the Hyfire and I put 12 volts to the positive side the voltage on the negative side is almost half or more and when I disconnect the wiring harness to the distributor all the voltage comes back (shorted module).:banghead::banghead:
Fast forward to today, I have had the engine completely rebuilt, installed a new trans and converter, got it all hooked up, got my new MSD RTR 8388 dist, didn't use the Hyfire CDI box, crank, crank, crank, "woof" took out the module.:banghead::banghead: When I check voltage at the coil (ballast bypassed) full 12 volts to positive side per MSD instructions, I have about 10 volts positive and on the negative side its about 4.5 volts and once I disconnect the 3 pin and all the voltage comes back (shorted module). I hooked up the Hyfire that I had and can get spark out of the coil but no start. This module wont be cheap to change, but I cant seem to figure whats wrong. Sorry for the long wind but its been very frustrating.