I measured the 1988 head that I got off eBay, and the bore is 88 mm. The head that came with the motor is 86 mm, so if I want to use the eBay head I will obviously need a new piston (Wossner makes one). The engine displacement calculator I found online said this combo would give me 523 cc. Do you guys think I should go that route (my life insurance is paid up), or should I try to find an 86 mm bore 1988 head on eBay? I think the sleeve on the eBay head is okay, but I don't have that much experience with non-coated cylinders. Is there anywhere I can send the cylinder to that can evaluate it? Thank you for the advice!