Well, I went ahead with the Sheldon method, and respaced to about 130mm, and now the 135mm hub slides right in if I spread the rear triangle a little bit with my hands. Alignment is still fine, and the stays bent in the right place.

I seem to have a very, very stiff frame for a steel frame, because it was a total pain to bend even 2mm per side, I had to stand on the end of the 2x4 with both feet in order to change the spacing at all.

I am leaving my wheel in the frame overnight to make sure the frame sets right, and after that it is time to paint!

As far as the fork goes, it turns out that the spacing was easy to stretch by hand, but the slots in the fork for the axle were too small - I guess vintage axles must have had a slightly smaller diameter. A few minutes with a file, and now everything fits fine.