That makes me think it is still grounding issues or a bad/marginal ballast resistor.

Putting a jumper wire from the battery positive to the ignition coil "+" terminal is the same as having the ignition key in the start position. This bypasses all the dash wiring. You could totally disconnect the bulkhead connector and the engine should start.
The issue with the ballast resistor is if it may be partly burnt and has higher resistance than normal. In the start position, power starting at the coil, power must run back through the ballast resistor to supply power to the ECU, alternator, and voltage regulator.
With a jumper wire across the ballast resistor, and the jumper from battery to ignition coil everything should be getting full power.
Now everything is eliminated from the circuit equation except the grounding paths. The ECU grounds itself through the case to the body (if it has a good connection), and the starter grounds itself through the engine block.
I don't know if you are using a battery ground wire that has a lead to ground the body, or ground wires from the engine block to the body?