what engines from what years will fit(bolt right in) in this frame if and or when this one is gone? also is it possible to remove the cylinder sleeve and replace? possibly with the stock bore and piston? friend of mine says bottom was rebuilt and top was bored out by PO. BUT here's the kicker - we have no clue what size the bore is or piston is from the rebuild or who the kit was made by because the bike runs strong as hell right now and didn't want to risk taking the top off. can someone please shed some light on this for me? Is this bike a ticking time bomb? Any answers ASAP would help! Please and Thank you!