if you really want a die hard track car (if that's the direction you are headed), I'd suggest buying one...as I know that the tear between track and DD is a tough one...also when you have to worry about wrecking your DD. Picking up a cheap, old RWD anything (toyota, nissan, mazda, etc..) isn't hard to do. Hell, I just picked up an AWD 96 impreza coupe for $900 down in Raleigh...food for thought
I know my DD lost the battle and I decided the subie would just be the track toy...the new DD is the toy hauler
As for the brake ducting...3" brake ducting would fit right up and its the common industry size. You will need to make tubed section for it to clamp onto...go ghetto and hit up home depot for parts