Ok, more info.

I pulled the backplate off and I found what appears to be a "staple" bent up with the ends curled like an S. I think it probably used to be some sort of retaining clip/ring/wire/etc.

Nothing else looked damaged but I have not pulled the cylinder off. I dont know how long that had been rattling around in there but I dont see any major problems.

Perhaps I will just put all of the ignition parts on the working mac given to me by my neighbor. I tend to spend more time trying to troubleshoot gremlins than I would have spent just swapping over to the other engine.

Any ideas what the problem could have been? I havent looked at the intake side of things, perhaps a leak somewhere?