Dude..... I know that the disc brake set up may look good and pending how good you are with spanna not to hard to convert but honestly weather it is track work or whatever there really isnt a lot of difference from drum to disc on the rear of a small car.

Reason being is that under braking either hard or soft, you transfer the majority of the weight to the front of the car (pivoting) meaning that your rear brakes do little. Unless you are going to have adjustable brake bias which most track cars will have you are better of spending your money on some go fast bits or for that point better front rotors or calipers maybe...... only a thought i hope it helps

Cheers
Peddler