I'm no Viscount expert, but are you sure it's 700C originally? The Viscount center-pull brakes should probably work with either and I thought they had 27s from the factory. I could be wrong. I'd find that out before you go looking at forks. In any case a 27" fork is not going ot be that much different. If you have 4mm more vertical travel in your front brake pad adjustment then a 27 fork will work fine.

Cheers,
Kar