The bike is now fully stripped. I've tinfoiled everything I could reach, then soaked the insides with meths, gave it a wipe, let it dry, then gave it a rinse with Hydrate 80 rust converter.
Top tube and fork blades were a bit of a surprise - I can hear some [rust?] flakes rolling inside them, yet these tubes are fully sealed and I could not get the rust converter into them.
If they are fully sealed, how did they manage to rust on the inside
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Front guard eyelets took some drilling, but I've managed to restore the threads to an acceptable level - good enough to hold a plastic guard.
Hardest bit was removing the broken dropout adjuster screw. Tried soaking in plusgas, then filing the dropout a little to uncover just enough bolt to grab with my pliers, but the bolt just stripped off. I then tried cutting a wee slot with a hacksaw and turning the bolt with a small screwdriver - just bent the screwdriver blade.
In the end, it was down to drilling the M3 bolt with a 1.6mm drill bit, freehand, with plenty of the world's most popular cutting liquid (WD40). I've managed to drill out the bolt almost with no damage to the threads. I should have been a brain surgeon with hands like that. Then refreshed the threads with a tap - should be good enough to hold the adjuster bolt.
Two holes drilled in the seat tube to stop the crack spread. Drilling Reynolds 531db was a very pleasant experience. If anyone wants a few extra holes in their frame, give me a call.
Overall, the bike's a bit of a challenge, but general condition is OK, assuming no more structural damage. All this work made me realise just how well preserved my Romani is!