2001 YZ426F - timing chain tensioner broke (we think) and piston, head/valves, cams, cylinder were all destroyed. We got a used engine off of ebay that has a bad 2nd gear. We're putting the good top end on the bottom end of the engine that was destroyed. We're planning on splitting the case of the engine that has the good bottom end to make sure no chunks of metal are floating around down there. Basically, it's a complete tear down and rebuild and frankensteining one engine with the other. What parts should definitely be replaced while we've got the engine completely apart (top end and bottem end)?