pstock

I originally posted this under Classic and Vintage, but as I look at it more closely it might be more of a Framebuilders question.

I have a rather plain looking frame that I found in NE France. what's interesting is what appears to be Rossin "R's" on the forks? and yet no other distinctive markings elsewhere on the frame?

Our first guess was that the bike builder had simply recycled a Rossin fork onto an unrelated frame.

But looking more closely, the interesting thing is that the "slipover sleeve" style of the front fork dropouts is unlike anything I have ever seen (in my admittedly limited experience with frames). and yet they seem to match the unbranded rear dropouts .

How common are these slipover sleeve type dropouts?
Could a frame builder have ordered them specifically to use with this mix-and-match project?
Does anyone have any photos of other elements of a Rossin main frame (Lugs etc.) that I could use to compare more further?

Peter