Are you certain what's on the old bike is a 7 speed free hub and cassette?
7 speeds can also be a freewheel. And those are very inexpensive and very likely any you can get today will still thread on to that same hub you currently have.
Or is it that your wheel is bad other than the free hub or freewheel being messed up?
Last edited by Iride01; 11-12-23 at 01:55 PM.