The Banshee and the RZ motors share many of the same components.
The Crankcases are almost the same – the Banshee cases from 1993 on are actually a little better as there is slightly more metal where the crank case halves join at the front and also around the crank but are interchangeable. If you were doing a +7 or +10 stroke its better for trenching the cases for the crank shaft. You can still buy them, and they are cheap. I bought a brand-new set just after christmas and they were only $500 including the dampers and damper spacers already pressed in.
The crank, clutch, primary, etc. are the same
The transmission has some slight ratio differences and you can make a really nice transmission using the Banshee 1st gear pinion and output shaft, with the rest of the ratios from the RZ350. That’s what I have in my track bike.
There is no oil pump on the Banshee and the mechanical tach cable hole is cast shut on later crankcases instead of just a rubber plug
The big differences are the cylinders and head as there are no powervalves, different exhaust mounts and the cooling/rad outputs don’t line up very well, and the stator coils and output is different
The Banshee cylinders are actually quite good for a track bike as there is a lot of meat for porting and if the engine spends its life above 6 or 7k you don’t really need powervalves anyway
When I order parts that are the same I generally order the OEM Banshee version as they tend to be cheaper than the RZ ones, although they are the same part. Go figure.
I think $2900 was a steal for that blue RZ. $9000 is just stupid, although there is one born every minute. I would think around $4000-4500 would be reasonable