help me find an electrical gremlin, please

Based on the tshooting guide from 67dart273 it all checks out with in spec so if there is no spark it "must" be the ecu. Must is such a strong word coming from a guy who admittedly dont know squat. But I do feel like I am finally accomplishing something.

Would it it mess anything up if I swap out the 4pin unit (presumably bad) with the 5 pin unit from the barracuda using the 4pin wiring harness. Don't want to screw anything more up...