A couple points of interest...
1. You say the engine is a 345. That engine was swapped in from some other vehicle as the 345 was not an available engine option for the Scout platform during the 800 production run.
2. You say the engine was running great, so it was time for a tuneup. Huh? If it was running so great, why fix something that isn't broken? I don't get that one.
You've identified your distributor as a Holley points unit. How positive are we with this identification? Perhaps a couple pictures are in order. There's nothing exotic about those distributors and certainly no need to source replacement caps from that particular light line vendor at what I'm assuming to be top dollar for the same cap that can be had for much less from most any reputable parts store.
Aside from trying to shoehorn the wrong cap on the unit, I can't think of anything else that would cause such poor fitment issues. There is an alignment notch cut into the lower surface of the cap that will only allow it to be secured to the distributor with the retention springs in one location.
