Are you saying that he was ridden in a curb with a thin twisted mouth piece?
If so, then i can see why he would be resistant in a bit.
A bit, like you describe, if I am reading your post correctly, is not a bit that would be used in any good training program, nor show legal, (judged event), but is used by some gymkhana people
Was it something like the fourth bit pictured in this link (311 )
If that is the case I would ride him in a bosal, or even a mechanical hackamore, if not comfortable using a bosal, and put some basic softness on him, although, if he ran through a bit, unless you also get him 'mentally soft, as well as physically, he can learn to run through a hack also, eventually
If no serious mouth damage is present, like a cut tongue, I would ride him bittless, going back to basics, and then re -introduce a snaffle, once he relaxes and learns to trust your hands http://www.mollypowell.com/products-bits.html