I'm currently running a 7-speed freewheel and 700x35 wheels. I have gotten hold of a pair of 700x23 wheels with a 6-speed freewheel attached. Can I swap one out for the other? If so, can I easily add QR to the wheels?
If they're both freewheels and the most common BSC threading, then you can swap one for the other. The only issue is if your 6 speed wheel was an Ultra 6 spaced freewheel (made for 5 speed hubs), then your axle length might be a little short and you'll end up with a slight wheel re-dishing issue. But 95% of the time this should work. And no chain issues in any case between any 6,7 speed setup