Thanks for the tips, I've never worked with OA before.

No, I don't have a bike to go with this. I found it in my LBS, they had some boxes of old parts and let me sift through them. I haven't actually tried it to see if it works, although everything seems to move the way it should. Feels very solid. It's missing the mounting bolt but otherwise seems complete. I might be able to get a Gran Sport rd which is supposedly in bad condition but could be a good parts source. Are the mounting bolts interchangeable? Any other parts? They look very similar.

I have most of a Record/NR group and some Universal 61 calipers, old Cinelli bars & stem, etc. I was thinking of doing a 70's build with them, but with this derailleur I could do a passable early or mid-60's build without too much problem. That leaves the frame, of course (by the way, I ride a 58-59cm if anyone has a lead on an older Frejus, Olmo, etc.). So far my oldest bikes are late 60's models (67 Atala Record and 68 Lejeune Tour de France), which are quite practical because it's relatively easy to find parts for them. Going back just a few years earlier the parts supply seems to shrink dramatically, and I haven't wanted to deal with the hassle of locating semi-rare and rare parts. But maybe this is a good opportunity to try something a little different.