Today I mounted the CST C-979D, 1-3/8" (37-630) tires I bought direct from China on those very rims.
It was a little tough getting them on (and centering the valve stem) because they were stiff and also quite grippy against the rim, being that they were new and clean.

The tires measure a full 35mm wide an hour after mounting with 75psi (will be lowering to 50psi for tonight's ride).

I've used these same Araya (and similar Ukai) rims on many bikes over the years, never had a problem with the alloy being soft and that's a good thing.
Their outside width is 25mm and I believe their inside width is 18mm.

I did once run folding-bead, 1-3/8" Michelin Hi-Lite Tour tires on these same rims. I was able to use 70psi but no more, lest the bead started climbing upward at some random position on the rim. It was safe long-term at 55psi though.

These rims weigh about 550g and the lightest steel rims are about 750g. They can be found in 36- and 40-hole in 27" size.