Yeah my old kx80 had a xr75 engine in it ( bought it like that... it was cheap ) the engine was mounted in front of the pivot ( I'm having a brain fart... can't think of what the actual term is )Hmmm you got me thinking, I'm not 100% sure if the bearings will stay in if there wasn't something there to stop them.
Worst case scenario you might have to cut a section of pipe to fit inbetween them as a 'retainer'.
Maybe someone will chime in with and opinion on this.