The issue with the charger isn't power, but rather aerodynamic capability. It would absolutely kill on an oval. I think we do these (if at all) as one-off events. We pick one car from each major manufacturer (the game already kind of does this) and go from there. I'm just sort of thinking out loud here, but let's see what happens:
Nascar is Ford, Chevy, Dodge, and Toyota, right? Well, no Toyota for a historic event, obviously, so we'll stick to three.
Let's have the mustang, camaro SS, and Challenger (though the charger really was designed for oval racing IIRC, it would massacre these two, and I'm thinking the Z28 was a road racer homologation special). We'll throw in the Pontiac GTO, as well. I'm not really up on my NASCAR history, so any suggestions are welcomed.
hp limit of 600 sounds good, assuming that they'll fit.
hp limit should be low enough to FORCE people to use full width slicks and WR, even if it isn't technically required. (This was the effect of my 200hp limit on the tiny terror spec; the weight limit and tire requirements were sort of redundant.)
Tracks: I'm all about some ring and some road racing, but I think Sunset infield is wrong for this; you can't go to Daytona for anything but the speedway in my mind. I'm thinking the two speedways and the most Watkins Glen-esque track we can figure out. I think Dirt mentioned Motegi East as a candidate recently?
Laps: We need way more than ten. We really want pit strategy to come into this, since that's the main thing that jumps out in oval racing (aside from the drafting, of course). I'm thinking either 25 or 50 would be better, depending on track, but make it long enough that everyone has to pit at least once.
Just some thoughts. Feel free to critique/criticize/flame/whatever.