The frame that Jon spotted appeared to be quite original and probably did date from the mid-to-late 50s. The odd shaped lugs were very common on Peugeots frames of that period and also on another of the Peugeot group of bikes the Meteore.
The Helium tubes are not quite gas-pipe..but neither are they chrome-moly.; they are in fact just Peugeots in-house standard high-carbon steel series. The Helium name is Peugeot's own brand..and again this model of frame could be found bearing a Helium headbadge and transfers. Helium bikes were supplied to retail outlets other than Peugeot ones in the days when brands were were supplied to specific concessionaires. The brand is still on the go even these days
It should not be very difficult to find matching parts on French ebay..Simplex gears, aluminium mudguards, a selection of dynamos and headlights, chainsets etc come up very regularly. In fact there is a superb old Peugeot chainset finishing later today.
The frame will weigh quite a lot - hence the heavy carriage charge. I guess really that the frame has, as the French say "..a certain je ne sais quoi"..a distinctive period charm.
Somewhere I have catalogues from this period so I will have a close look around.
Norris Lockley
Settle UK