My take would be that if you're going to the trouble to restore and ride a Holdsworth Whirlwind, it's really for the aesthetic value of the bike. So you might as well get the nicest looking components you can afford. A 1958-edition Allvit and a similar era Campagnolo Gran Sport might have similar shifting performance, but I think the Gran Sport just looks a lot prettier and only costs around $60.

A nice thing about the Whirlwind, is that it was always highly customized to the rider's specifications, as the Holdsworth catalogue makes clear. Mine has a CO2 inflator braze-on and little wheels for the derailleur cables--but no braze-ons for the brake cable! So I think that you can pretty much choose any parts that were available in the (very extensive) Holdsworth catalogue at the time, and it would be 'authentic'. Great bike, really love riding mine.