Thanks all for the helpful advice! Looks like I'll be focusing on changing the freewheel and RD instead of the chainrings (I'm leery of trying to drill out the riveted chainring bolts).

From FBinNY's response, it seems like I'll need a long-cage derailleur to handle the 32-tooth large cog on the new freewheel. It looks like there are some SunTour mountain/touring bike RDs from this era on eBay (models like the XR 100, XCM, XC, and XC Pro). Does anyone have experience with those and whether they're compatible with Accushift index shifting?

Also, some of the Suntour mountain bike derailleurs on eBay are listed as "direct mount" derailleurs. I searched around a little and can't get a clear understanding of what that means. There are references on the web to new "direct mount" technology from Shimano announced in the past couple of years, but that doesn't seem to apply to mtb RDs from the late 80s/early 90s.

Any advice on whether I can mount one of these older Suntour mtb derailleurs (XR 100, XCM, XC Pro) on my bike using the existing derailleur hanger?