@BigDB67 no need to buy the brakes until you settle on a wheel size; you have to measure from the brake mounting hole to the braking track on the wheel to get the value you need.
If you don't want to change wheel size (and why not? You can fit a larger diameter tire in with 700), Panaracer and Continental still make good 27" tires. The era of good 27" rims is long over, but you can still get basic aluminum extrusions from Weinemann and a few others, that will be vastly better than the rims you have. If you build your own wheels, the is no reason you can't use modern hubs and 27" rims, for maximum retrogrouch-ness.
Whatever you do, new calipers will be a vast improvement over the ones that are likely on there. I agree with
@qclabrat , though. I would buy a basic set of 27" aluminum wheels, get some Panaracer Paselas, and a couple of new brakes of appropriate reach, in addition to whatever else (paint, polish, etc) you are going to do to the frame. Wheel building is a great skill to learn, but you will never come out ahead vs the same thing pre-built.