martyquaver

hi guys, looking a bit of help here, i have a 1987 yamaha fz 600 air cooled bike, seems that the piston rings have give way on me as its spurting out oil through the crankcase breather pipe, would anybody be able to tell me what other engine would fit into this frame, ive been told a 1000 exup engine would fit, just looking to see if amy others would also, any help would be much appreciated, thanks.