Going 700C clincher shouldn't be a prob. I'd check eBay for a vintage wheelset as opposed to relacing. Probably cheaper than the new rims/spokes and keeps the orig. wheelset intact.
You should be ableto get a "Ultra" 6 speed freewheel on there but if your gears are 14X31 I don't know if you can get much lower.
A 39 tooth small ring front chainwheel might be helpful. You can get Salsa brand ones for reasonable money and keep the Campy markings on the crank arms and big ring. Probably can't get much smaller than 50T on the big ring but a 39X31 "climbing" gear should do the trick.
Post pics.
