the 650's, cx or gl, will drop onto the 500 frames with a modified 500 stamped steel hanger. you cannot modify the gl hangers as they are cast.That Nimbus is a 650 motor, right? If it's not terribly difficult to do I might be tempted. My problem would be sourcing a manual tensioner, I don't see any on ebay and I think the Turbo 500 I have is automatic.
@SirFoxx I'm putting my 650 into a 500 Turbo frame. I think the 650s drop into a GL frame with modifed GL650 hangers but on mine I may be fabricating completely new hangers because I hate the stamped sheet metal ones. What are your engine hanger plans looking like? If you've caught Murray's attention I'm sure he's discussed it with you I'm just curious.
there are 4 bolts that hold the hanger to the motor. I believe the lower set needs to get modified--you cut the collar that the bolts go through off the mount, get new collars and move them down like a 1/4" and reweld them. its a very simple process. the reason for doing this is because the upper part of the mount that bolts to the frame is very different between the 500's and the 650's.