This is what I would like to do: My R90/6 smokes a little more, struggles a little more, etc. I would like to refresh the top end. However I would like a little more guts so I would like to swap out the cylinders and pistons for those from an R100/whatever. Can I swap out cylinders/pistons from some of the later models in order to take advantage of the nikasil cylinders? Maybe a better question is what WILL NOT bolt on? Can I still use the R90/6 heads with an R100/? and also would anybody recommend a place that you can send your heads out to to freshen them up (newer hardened valve seats,etc.)? Thanks for your brain power and expect even stupider questions to follow! Bob h.