I don't understand why the rotor is so difficult. Pick a D-S II vintage vehicle and get the cap & rotor for it. Do Not tell the counter guy/gal what it's really going on, that just confuses the hell out of him/her and messes up everything. I've found that this is particularly true in the mass market chain stores, which I try very, very hard to not patronize any more!
Do your research first, then get the parts for the application that you've found. This is the way that I've done things like this for 20+ years.
According to Rock Auto the Standard Motor Products D-S II cap part number is FD161 and the matching rotor part number is FD117. I found these numbers by looking up a 1980 Bronco with a 5.0L.
Summit isn't selling you anything special or different if they are supposed to be stock replacement parts. You don't have to have their parts exclusively for it to work right, not if you educate yourself on what parts to ask for first.