For your red bike, I'd suggest 622 mm wheels (the "700c" size") which is 8mm smaller diameter than your existing wheels.
Its your choice if you want to go for a "road 700c" or a "MTB 29 inch" wheel, which will be governed by the clearance between stays and between fork tines for the tyre. Both have the same rim diameter, but will be available in different rim widths (where the tyre lies) A wider tyre will sit better in a wider rim.
Given your earlier statements, I'd go with road bike 700c wheels, with gum-wall or tan side-wall tyres to maintain the historic look. A wider tyre would also look more original than a narrow, so 28mm as a minimum, and 35mm~38mm would be great.
Not a product rec, just an example.
- With disk brakes, you can run a pair of 650b wheels with larger rubber on them, if that is of interest.
- Rim profile will be important too - you ideally want some box-section rims for the look, not deeper-section rims. This will be very hard to find in a MTB wheel and somewhat hard to find in a pre-built road wheel. So you may have to build your own wheels with older style rims onto disk-based hubs.
- Rim material - Your red bike would have had distinctive steel rims which are a shiny chrome, or a rusty steel. A more modern bike would have alloy rims, which have a dull grey patina clearly visible on the brake track and no rust. Since you're not using the brake track, it may be worth either polishing the alloy rim to a mirror finish, or exploring some kind of spray-on chrome finish for the brake track.
- Its going to be impossible to hide the disk brake rotors, so you might choose to distract by fitting items like a gutted bottle dynamo housing, and an old school front headlamp (which could have modern LED inside.) You might even hang a set of vinyl pannier bags off a front rack, but that all adds frontal area and increasing drag.
- Another option is build the mounts for common 140mm rotors, but to fit an interposer adapter and run a tiny 120mm rotor, which would have a "side area" of 113 cm^2 vs 153 cm^2 for a 140mm rotor. Also look for a rotor that has more cooling slots so its less to see. You could even fit plastic spoke protectors on either side of the front wheel to help hide the brake rotor from the right-hand side, though that would also look weird.