Re:
I don't go for 100% period builds. Period frame, forks, mechs, chainsets, brakes, wheels, stems and bars.
Certainly not chains, cassettes/rings, cables or brake pads but nothing that wouldn't look out of place. As for headsets and bottom brackets, unless they're NOS and therefore very expensive, you're taking a risk on a bearing that may last a week. Which is probably half the lifetime of a new UN55!
As for saddles, ive used Flites and Rolls for a looooonnnngggg time and I use those on all my bikes even modern ones.
Mike