50cm will probably be too small, but ‘yay’ in principle – older steel frames can be great. I do most of my road miles on my ’92 MBK HPF frame (albeit with more recent components, and somewhat wider gearing than it originally had), and I find it’s very comfortable, even on it’s mismatched low end wheels. You might find some stuff a bit of a challenge to service / match up, but if you can live with compromises you’ll be fine.
(Friction shifting will get you out of almost anything! 😛 )
Granted, I am a bit of a flat-earther about bicycles, but I do love the feel of a good, well thought-out steel frame. Indifferent steel frames are out there too tho’ – so good luck picking through them.