I dont know why some body would use a banshee. Suspension has come a long way since the late 1980's. If you just going to do a hack job then go for it. If you want a nice machine then shoot for something more modern.
A raptor 660 would be about the best one to use. Modern suspension and it has a lot of room where the stock 660 motor goes. A yfz frame would be shorter and more cramped.
03 Limited Edition Raptor Hot Rods 720cc Stroker, Megacycle x-4 cam, Sparks 6X Big Core Exhaust, 35mm Keihin FCR's.
97 Yamaha Banshee - F.A.S.T. Dune Ported 4mill Stroker, CPI Pipes, Keihin PWK33's, Direct Drive Lockup,
158 main jets, CEL Needles on the middle clip, 45 Pilots.