Help please, plug reading wizards!

OK you just said you have the HEI conversion.
Now you need a straight wired e-coil to go with that to give you the hot spark. HEI needs the e-coil, not the old style tower coil like comes stock.
The Magnum V-8 engines have a very similar-looking e-core coil as the F-150 shown. It mounts on the front of the accessory bracket, so an easy pick. Clip engine harness to get the mating connector. That keeps you Mopar for those who care (as if Mopar makes their own coils ... snicker). I always recommend the GM 8-pin HEI module (1985-95 V-8) as you can also grab their coil and the cable which connects the two, so a simple click and play. Of course also snip the wire at their distributor pickup to get that connector.