The size I think works best with these are actually 27 x 1" (not 1/4 or 1/8) just plain 27x1. With care in fitting to the rim, they seat well and look just splendid. And the ride is excellent, too. These are, I think, among the best looking and riding rims every made and they look so much better with tyres that emulate the classic Dunlop HPs. Most 27 x 1 1/4 are just too "chunky" looking. Here in the USA, you can still get NOS Schwinn 27 x 1 HPs (90 psi). Do NOT try and inflate any tyre on these Dunlop rims above 90 psi.
I just got a pair (and another pair is up on eBay right now) for the Dunlop HP/Campy high-flange wheelset I've decided to fit to my '67 Holdsworth Super Mistral.
Here are pix of my '58 RRA Moderne with Dunlop rims and 27 x 1 tyres:
http://www.wooljersey.com/
My '48 RRA with Conloy Asps also is shod with 27 x 1s.
Peter Kohler
Washington DC USA