I'm brainstorming with the rest of our Club Race board to come up new/better ideas for races
What ever you do, don't have mandatory pit stops. There is/was a 4+/- hour race at WGI that I used think would be fun, but didn't go simply because they required 2 stops, 5 minutes each. That's not an enduro, that's a couple of sprints shared by a couple of drivers. If I understand it correctly them roundy round guys from down south on TV every sunday often do mandatory stops, you wanna be associated w/ them?

Enduro's have pit stops that require strategy (ie, long enough to force every car into the pits at least once and force the re-fuel/driver change to have some pre-race planning). Anything else is a sprint race w/ some interruptions.