You may be able to get a good used wheelset with 27" rims by just looking at CL for used bikes. These often include the freewheel.
Happens all the time. Or, new ones are pretty reasonable from Niagra, other places.

I'd try a 700c conversion first, see if those calipers will adjust down the 4mm like others have said. Doesn't look like it from the photos.
If so, Maddux wheels from Bikewagon are a good value. There are plenty of 27" wheelsets out there.