Putting a 700c fork on a 27" bike isn't going to make that much difference to the steering if you're using 700c wheels. The front will sit a little lower, increasing the head angle a bit, but not enough to change the handling a whole lot as long as you can get an approximate match on the rake. In other words, don't put a 43mm rake racing fork on a Raleigh Super Course. Also be sure your brake calipers are long enough to reach the 700c rims.