I can tell you this much, the glow plugs Bernie sells at coxengines.ca fit the Norvel as well as his clamp rings if you need an extra.. Those are good plugs, in my experience.
In a pinch, any old Cox .049 head, as well as a Nelson head/galbreath plug fits and runs well on a Norvel. It just looks funny. TD Hi comp would, of course be best. If you don't get a starter spring, it's a lot easier to get cranked for its first run-in with a Babe Bee head too.