patelladragger: if you put only one disc, be sure to put more material on the flat part of the brake shaft and the brake stops up and bottom on the left, because i don't think a single disc is thick enough to be in the range.

one thing you guys may want to try, or maybe you already did.
place two 3-4mm washers above the fuel tank ears. your tank will sit 3-4mm lower. but be sure that the tank isn't touching the chassis!