You should be able to still run 700 wheels if you could find a set of the old school onzo brakes. You know the ones that you moved the brake pads up and down on a shaft. I know for a fact that they have enough reach to let you run 700 wheels on late 80's Gaint Iguana mtb frame.
A number of cross racers in the Orrville area were running this type of set up a couple of years ago, me included. A few are still running single speeds set up this way.
Orrville Cycling and Fittness may have a set of them or a knock off of Onza's sitting around. If not I bet Dell's would have a set.