No worries, we did the GT300s base model a little while ago, but just revised them, biggest problem is the ARTA. With RH tyres it's so out of balance, but put on sports soft and its a different car. Some tracks it can be setup to be quite well balanced (on RH tyres), but go to another track and it falls to pieces.
Let me know what you want to do, I'd recommend putting it on SS tyres as with these, stock, it's not that much slower than the other cars. Once it's setup, it should be bang on the pace.
Alternatively, there's other low powered cars that could take it's place in your series, maybe have a look/think about using another car.
Or, alternate choice no 2 - car equalisation is always subjective, people are going to argue / question no matter what, one method we use to stop this is to make everyone drive each car. So if there's 8 races and 4 cars, everyone drives each one twice, or make it 8 cars and 8 races / tracks and leave the car choice up to the participants.
This way everyone has the same "equiptment" and no one is worse or better off than another.... hope you dont mind the suggestion, it's worked very well for our championships and alot of members seem to like it..