It looks like it could be an 87. Do the foot pegs bolt on or pin on? 86-87 bolt on, 88-89 are pinned. The 85-86 cylinders have casting lines on top of the water jackets just below the head & the 88-89's don't, but I'm not sure if the 87 cylinder has casting lines like the 85-86 or not:
Pull the reed cage & look inside to see if there's two intake bridges, 87-89 had these & the pistons have a window cut into the intake side. The 85-86 is a just a big hole & the piston has a half moon cut out of the bottom of the skirt.
