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dcdavys ; generally, I concur with Kontact's recommendations. If you like the bike as-is and it fits your needs, provided the rest of the drivetrain is sound replacing the existing freewheel with a modern SunRace freewheel (they have a good rep) may work quite well, at least for the short/mid-term. I've read accounts of people having had excellent results shifting SunRace freewheels using Suntour equipment in indexed mode. Because SunRace freewheels are Hyperglide "compatible", they have similar shift ramps shaped into their sprockets. Reputedly shifting is considerably improved.
I'll see if I can find some of the info I've seen previously on that combo here at BikeForums. If I can find it, I'll post a link here.
Can't give you personal insight as to how well that combo works. My schedule for the next few months means that my planned SunTour 7-speed Accushift build is going to be "back-burnered" for at least that long. But a 7-speed SunRace 13-24 or 13-25 is what I plan on using for the freewheel. I have both, but the RD I'm planning to use specifies 24T as max largest for indexed shifting and I haven't decided whether or not I want to "push the envelope" or not immediately.