I need to replace my rear wheel and right now I have an old freewheel cassette(Shimano). When I replace the wheel I want to upgrade to the cassette set up. My bike has the old style index/friction shift lever on the downtube (which I don't want to change). All the wheels I see are 8/9/10 speed compatible. If I use an 8 speed cassette and just limit the rear derailler to eliminate the low gear, can I still use my existing shifter? Thanks in advance.