Did I hear some one mention RD400 basket case?...lol.
Greg, if you are looking to move it on to a good home please pm me.
Barrel/Bore spacing and hence crankshaft spacing on all of the horizontally split air cooled engines is the same. R5 through to the G RD 400's. I wouldn't be surprised if the RZ motors ran the same barrel spacing, the difference is the cylinder base stud orientation.
The development that is taking place on the RZ250-350 motors because of it's placement in a popular American non-power valved ATV is quite astounding. The new DM series are producing on the dyno, similar power and torque curves to the 1000 cc R1 (trinity racing 610cc Dm Cheetah)
Quite amazing for an engine and gearbox you can carry under one arm