I'm looking seriously at an R65 which has a replacement engine from an R90. I've owned a bunch of BMWs but never one with a different model engine replacement and have a few questions. I think I know that the R65 has a lower final gear ratio but does this ratio difference happen in the rear end or in the transmission. Also, is the ratio difference significant enough to be a concern? Are there any other issues that I should be aware of? I'd appreciate any advice that you have before I make the purchase. Thanks. Jim