the small problem with respacing your axle to allow room for a multispeed freewheel is that the bearings are sealed, and the axle cannot be moved from side to side to allow for more spacing on one side than the other. So, if you can add enough space on one side to clear the five speed, and still have enough room to put a nut on (and can stretch the frame to the new spacing), then you are all set - don't bother with the fact that one side is longer than the other.