Here we go, trial fit with the 26 x 1-3/8" wheels. I think my cranks are buried in the shed so I threw on this Rudge one that SWMBO doesn't know is under my socks in the drawer.
Now, I was expecting them to look a lot smaller than they do. I still need a smaller axle to fit in the rear dropouts, but they fill the forks quite substantially. The 27" tyre is about 35mm bigger in total diameter, so it'll be a squeeze if it does fit. I'm wondering if tubulars might not be such a bad idea after all.
Oh, and weights. The frame/fork/bars/saddle combo weighs just a little under 5kg. Those wheels weigh a whopping 2.6kg for the rear and 2.3kg for the front!