Page 99 of Radio Race Car International.
A few GTRe's run the Schumacher BTCC in the UK, sorry, don't know anything technically about them but I do know guys were using brushless systems and not all ran 3 speed systems.
The cars looked to be a bit of a handfull so their results aren't great.
The rules for the championship are here (Just so you can see what spec they could be built to);
GTRe Rules For BTCC
Results can be found here;