here's what's possible with that frame (and as I mentioned if you go with a newer cassette hub and derailleur hanger, Shimano index shifting, though friction works great...)



don't let people dis your bike


ps - with long-reach brakes, you could even go to 650b on the wheels, giving room in your frame for big tires
whatever you put into wheels, you will always have them
only skimp to pre-made 27" if you're on a tight budget - any 120mm off-the-shelf freewheel wheelset will fit an Ultra6 freewheel

pss back to wheelbuilding.
Don't know how your LBS works, but mine will take 80% off wheelbuilding labor if you buy all the parts through them.
LBS can order anything from anywhere.