You appear to have got yourself quite an interesting and yet mysterious frame there, Peter.
I have three FOLLIS frames with the same head lugs as yours..and all of varying quality...from mid-range to almost and even possibly pro standard..
It is difficult to identfy Follis frames from these lugs, but I think it reasonably safe to say that your frame could be a 1950s or probably no later than about 1963. Jean Forestier, one of the quality regional French Pros won the Paris-Roubaix in 1955 on a Follis with these head lugs.
My first Follis with these lugs is mid-range..possibly not even chro-moly such as Durifort. The actual head-lugs are attractive. but the other lugs and pipes are not so. Seat stay bridge is curved and the rear drop-outs are pressed plate of quite an unusual design. The frame is light metallic blue. As I recall it, the head tube was dark blue, with the FOLLIS and LYON picked out in the same colour.
My best FOLLIS of this type is quite another story..very light, quite elegant and well-made. It is very similar to your frame..from what I can see the lug set is the same..almost like simple Prugnat, and appearing possibly to be cast rather than pressed ones. Drop-outs are Simplex like your frame. The finish is light metallic blue with chromes-head-lugs and three-quarter chrome to stays and forks. It is an excellent frame in all respects, except that the transfers have gone. I think that metallic blue must have been Follis' team colour..akthough the team's shirts were dark green.
If you visit my Flickr photos and sift through the various entries you will
find the Follis section with a couple of machines in there. Unfortunately I
still have to load photos of my best Follises.-
http://www.flickr.com/
I bought mine from a seller whom I trust who lives on the Riviera..he told me that it had been a frame built for one of the Independents or mercenaries who rode for 'primes'. Certainly the very low number on the fork end - 18 - makes me think that it was one of a small edition.
One of the details of your frame that fascinates me somewhat..is the treatment of the wrap-over top-eyes, that appears to be tubular ones finishing in points. Those are quite unusual on any fraame ,but I have seen them, once, on a URAGO, and another time on another frame that I own, but whose make I am uncertain of.
I think you have a very good frame there, one worthy of being properly renovated. Unfortunately FOLLIs' seat transfers of that period were big and complicated and probably very expensive to recreate.
Do you haave the forks to the frame? If I have time..and can actually find my top FOLLIS I will check out the forks..and the crown.
Hope this info helps you make up your mind about what to do with your frame..
Norris Lockley
Settle UK