Am I going to have any issues fitting a new 7sp cassette like this?
If you have a male threaded lock ring screwing into a female thread on the freehub rotor and one of the splines is narrower than the others, you have one of the transitional 7-speed hubs which had both male thread for UG and female thread for HG, and you can fit a modern 7-speed HG pattern cassette.
If you have a male threaded lock ring screwing into a female thread on the freehub rotor and one of the splines is narrower than the others, you have one of the transitional 7-speed hubs which had both male thread for UG and female thread for HG, and you can fit a modern 7-speed HG pattern cassette.