Here we go with boneheaded question time.
Old hubs and cassettes. What can be made to work with what?

6 speed, 7 speed and 8 speed. How far up the evolution chain can they be taken?

Can, for example, a seven speed rear wheel be be fitted with an 8 speed cassette? Does it need re-dishing or a new hub/Wheel?

Would be interested in knowing the same for a six speed wheel too.

Many thanks in advance.

6,7,and 8sp screw on freewheels can be swapped, but may need spacers swapping/re-dishing(and are usually poor quality hubs).7sp cassettes can be fitted to an 8/9/10sp freehub with a spacer, but not the other way as the freehub is too short.7sp freehubs can be swapped to 8/9/10sp, but can be a bit of a faff with spacers/dishing/cone-seal sizing.