One option would be to go to harris cyclery (sheldon's old bike shop) or your lbs and get some nice alloy rims there and thread on a 6spd freewheel. If you have friction shifters, it shouldn't be a problem. If you have indexed shifting, it get s a little more complicated. You'll need to get a new chain if you're getting a new freewheel cassette.
It's a 6 speed friction DT shifter mid-80's Expedition. It has a low-end non-matched wheelset now that I would like to replace. The Suntour RD has been replaced with a Shimano STX. I'm not a Tourer, but my understanding is that the touring wheelset needs to be more heavy duty then standard wheelset. It probably came with Araya rims with Suntour ir Sugino hubs when new. Just wondering what would be a good match for this bike.