I saw a post somewhere (I'm old and I can't remember where it was) inquiring about convertibles at the spring track day. So I sent a question to Reon and here is his response:
Hey Stephen,
The track doesn't require roll cages for convertibles but the top will need to stay up while you're running the vehicle. As far as the drag strip goes, you would have to consult the NHRA rules. I believe 6-point Cages are required for vehicles quicker than 11.50. This is (of course) if we end up running the drag strip that day.
Cheers,
Reon
Also, helmets are required.