I have recently come across a 86 Peugeot PH 10LE bike in my size for an ok price. It's all original and would need some upgrades in my mind.

I've heard of a few gotchas on these bikes, the major one being the seat post, but my main concern is upgrading the rear derailleur and if a current model Shimano (105 for instance) could be screwed into the derailleur hanger that comes on the bike without any issues.

Any insight would be appreciated.