From what I can understand of this set-up, you could completely remove that ECU and leave it on the fireplace mantle and it would still run. It simply isn't being used by the truck any more.

As the the vacuum test for the advance, all I could tell you is to apply some vacuum to the vac advance port on the distributor and make sure it's adjusting physically, and make sure it doesn't lose vacuum. Someone who knows (anything) should be able to pipe in with a procedure or settings to tell you what you should be seeing.

I believe the reluctor could in fact go bad. How? What? I don't know. It's a black science in there to me.

I'd still have a look at the running engine in the dark. I've had bad spark plug wires right out of the box that were shorting before, and it showed up that way - nice blue arcs in the dark.

Good luck, my friend.

John B.