Yup, very magnetic, definitely steel.

I may be getting round to servicing the headset at some point so hopefully I can find some more clues about the fork then.

My general suspicion is that this sat in a shed for a good period of time (with the sun on it on one side) and was pulled out at some point (potentially not all that long ago) it got a full referb (it's been done properly, insofar as there is a decent quantity of grease in the stem and seatpost etc) and that's when, for whatever reason, the forks got swapped.

The collection of finishing gear is close to what you might expect (assuming it was put together by a French LBS) with the spidel / simplex derailers, mavic hubs/rims and Atax stem (I know Simplex and Mavic were part of Spidel: https://www.disraeligears.co.uk/site...railleurs.html), but it also has suginio cranks (should perhaps be stronglight), a gipiemme seatpost and Galli brakes.

I'm still keen to hear anything about 'Cycles Bolley' they are otherwise entirely invisible on the internet, which given the number of bike enthusiasts seems somewhat odd!