Yes for 451 wheels you need calipers - but very long reach ones. Last time I looked there was only one caliper on the market with the right reach - the Tektro R456 I think they are called (but look back in this thread to confirm).
Oh, and there is plenty of clearance for 451 wheels. I have mudguards on mine too.
Without mudguards, you can actually fit a 22" wheels in a swift, making them UCI legal, and swifts have been used with 22" wheels for track racing.
Rickybails,
Thanks once again for your VERY helpful bits of information. Since I've never even seen a Swift other than web-pics, all I have to go by is info I've found on the net, and the helpful tips/advice here on the forum. I'll be sure to pay forward my findings & experiences with my project here in this thread.
Thanks again!
Paul, that incarnation of a Swift you've built up looks like a real touring machine!
Rgds to all,
K.