Make sure the seat- and chain-stays don't interfere with the cassette and chain with an 8 speed cassette. I have a Raleigh Grand Prix from a few years after that one and my modern cassette hub didn't work. I am going to use the stock Normandy hubs laced to 700C wheels when/if I get around to building it.

Edit: Sun CR18 is made in 27" size, but I doubt you will find it pre built with a cassette hub.