That's gorgeous! I love the lavishing of care upon it even though it's "only" HiTen steel.

In the late 70s and early 80s, several Japanese companies were heavily investing in R&D to make better seamed tubing. We usually assume "HiTen" and "seamed" mean "junk", but the technology was developed to make very high quality multi-butted seamed tubing much more cheaply than similar seamless tube. I think bikes like these are the result... it weighs about the same as my similarly-cobbled-together early 1970s Columbus-tubed Italian bike.

I really hated those DiaCompe center pivot calipers, once upon a time. In fact, I replaced them on my partner's mixte. Necessity forced me into trying one on the front of my own bike, and I found that after completely disassembling, cleaning, polishing, and lubricating it that it's actually a very nice and moderately lightweight brake. The key was a light coating of grease on every surface that rubs against another... both sides of every surface in the center pivot stack, as well as on the return springs where they rub against the nubbins on the arms. I liked it so much I sourced a matching rear caliper and polished it up too!

My only quibble would be with the rear brake cable routing. I'd swap the barrel adjuster and the anchor bolt, then route the cable down and around in a big loop, entering the caliper from "beneath". It would look much smoother and probably work more nicely, too. On these Dia-Compe 500 centerpivots, you can just unbolt the barrel adjuster and anchor bolt and swap them -- they have the same diameter holes.