Don't let my experience discourage you.
MANY have had success putting smaller events together, particularly the local F-Body guys, so obviously it can be done. One of the first "shootouts" NorCalLS1.com (their name at the time) had was down in Bakersfield. Crosswinds would kick up at times which affected faster cars, but there weren't many.
Bakersfield is a fine, simple venue, apparently lacking in the BS department when it comes to renting it for the day.

Limiting it to GN vs. Mustang would be good for controlling the # of entrants, though honestly, I believe you would be lacking in TR representation without focused outreach to the So-Cal folks, and also the NorCal folks who do not participate in regular communications with web-based TR enthusiasts on BBS or local club mailing lists. For instance, some of the faster TRs in this area, who are more or less "regulars" at Sac, want nothing to do with the NorCalGN club for some reason. Dunno why. Weird. The political BS does fly at times, and as with anywhere ugly personality traits can appear, but it isn't a regular issue.
Anyhoot, make some phone calls and run some numbers to see what you think. Potential cost items are track rental, EMT/Fire, VHT, food vending, lighting (if at night), insurance rider if fast cars come, cleanup, port-a-potties, cash purses, trophies. Possibly business license if any profits are taken, which could also include dealing with taxes owed on gross receipts, then filing for a tax refund. I had intended to turn all the $$$$ over at the end of the day to the Class winners.
Running a pair of cars every 30 seconds, which is fairly easily attainable, equates to ~240 cars per hour. Many folks won't be happy with that wait, so limiting the cars to ~100 would make for reasonable waits for those who hot lap, particularly since ~1/2 won't. That makes for a ~10 minute wait between laps. If you have 4 hours of open running, thats a huge # of runs. Then the last couple hours can be running ladders for various classes.
Class identification can get tricky, and you need to get trustworthy rep's from both sides to properly classify each car. Most don't want to bracket race, preferring heads up, but a back-halved TT car vs. an average street car with bolt ons would be silly. Index was the way I was leaning, in mostly 1/2 second classes to begin with:
10.00-10.49
10.50-10.99
11.00-11.49
11.50-11.99
12.00-12.49
12.50-12.99
13.00-13.99
14.00-14.99
15.00+
A couple were a bit sparse at the point the event died, which would have led to combining classes. At the time a majority of the cars were in the 11.50-11.99 and 12.00-12.49.
Anyhoot, keep looking into it. I'm getting old and grumpy, so pay little mind to my complaining.
Dean