Late to the game, Brit car fan and racer, and hell, I don't see anyway that car (the MG could compete in A. You can't fix basic suspension issues with the car and it's never going to make the power it needs.

If you are serious about a Brit car in B.....there is always the TR7...lol....laugh, or maybe don't... 2.0. Can be made to handle. Decent power torque out of teh stock motor (90ish stock hp, 100ish stock torque), came with Bosh L-Jet the last two years so you have the ability to put a standalone on it and tune. TR7s are cheap/free and parts are plentiful.

There are a lot better choices but if you love Britstuff, that's probably the only oddball Brit car with a chance in A/B/C.