An old wheel with a 7-speed freewheel gave up the ghost and isn't worth rebuilding. I have a similar but newer wheel that has an 8-speed cassette. If I put a 7-speed cassette with a spacer on it, can I replace the defunct wheel with the newer one and still use the current 7-speed shifter and derailleur? Everything is Shimano on both the new and the old wheels as well as the shifter and derailleur. Is the spacing the same on a 7-speed cassette as it is on a 7-speed freewheel?