The SGT classes I think are rather simple. GT500 - Air restricted to 500 hp (some heavy cars get a bit more), GT300 is 300hp. The current LFS GTRs are 490hp.
I'm not sure about Britcar but some cars are ex-DTM and the TTs were 4WD IIRC.
I'm not sure about Britcar but some cars are ex-DTM and the TTs were 4WD IIRC.