Ant and interested others,
I figured that Lee or sombody would have posted this by now.
We mainly run the ROAR rules and classes. The 1/8 GT is a seperate Kyosho class. We also somtimes run the mini coopers from the Tamiya TCS rules. There are also the F1s, but I don't know which rules. In nitro last year, we ran 1/8 GT, 1/8 open, 1/10 nitro TC(.12) on a regular basis. In electric, 1/10 TC(13.5/23), 1/10 TC(open mod), TCS mini, but the electric did not run every race weekend.
You can check out the ROAR rules at:
http://www.roarracing.com/