Beautiful conversion... guessing that you had one of the fairly uncommon Swiss threaded bottom brackets which fall into that 1978 date estimate as a Peugeot of that era would have been French or Swiss threaded.

I have never come across a Swiss bb in all my years of turning wrenches and I have worked on a lot of Pugs... it is more likely that I will come across something like a Thompson bb.

The only difference is that French cups are right hand thread on both sides while the Swiss cup has a reverse thread on the drive side like an English cup, but with metric threading.

A Swiss standard would have made sense in what is predominantly a metric based world and with a left hand fixed cup you don't risk having your fixed cup unscrew itself during your ride.

In any case... take good care of that bb and it will serve you well for a very long time and start looking for a replacement as you aren't going to be able to pick up a Swiss bb at the LBS.