Re:
Took a closer look at some of the bits today.
Most of the Shimano components (such as the cranks, pedals and brakes) seem to be dating back to early 1989 (NA, NB). Perhaps the s/n reads June '90?
BB has a threaded axle and has lost its smoothness.. BB shell width is 68mm, so that's probably not Italian threaded. Headset reads like a YST on the top nut (for 25.4 stem, so 1").
I have no idea what make the stem and bars are.
The chain is a Uniglide (on a Hyperglide cassette), rear mech rd-m732, front mech fd-m735.
I'm wondering whether a 29.4-27.2 shim will work in this strangely shaped seat tube.?