The one disk is a dragrace thing and I think means he has put a GXF750 motor (Katuna) in it. Do not mean to defend the idiot but you have to feel sorry for the kids that rode th short bus to school.
There are plenty of bikes with a single disk out there and none of them pull as a result. Since the rotors and calipers are both mounted to the fork there is nothing to cause an exteral torque on the fork that would cause it to pull when they are applied.
Oh yeah and 90 forks in the us were the standard units not USD. I'm not sure why but between 90 and 93 there were a lot of differences between the GSXRs in different markets (for example the US didn't get water cooling in the 750s and 1100s until 93).