Had an electrician go through the entire place when we first bought the house so we could get safe three-prong outlets in place of the two-prong ungrounded outlets that were originally there. Didn’t do a full rewire because there’s no ceiling access - originally, the only heatsource for the house was electric radiant ceilings, though a couple baseboards were installed at some point after initial construction. The wiring for the sunroom’s A/C is run through a conduit on the outside of the house. I replaced the original through-wall unit shortly after we moved in, and I’ve seen that whole circuit.

What about the interior wall, against what used to be the exterior of the house?

I’ll recommend some modern keyboards that are suitable for your retrokit - I’m a big fan of Unicomp keyboards myself, though they do not do N-key rollover, if that is something important to you. Their lighter shade (they call it ‘white’) is more of a grey than a beige.

You may also consider USB keyboards that can handle P/S2 protocol with use of an adapter (not all of them can do this very well). I have a WASD keyboard for my modern PC that I sometimes also use with my older machines. I would recommend them, but they appear to be out of business.