The 35mm adapter seems to be a Rolleikin, made by Rolleiflex. I had one in the 1950s and it worked very well. It produced 35mm in a "portrait" mode and of course I could sync with strobe a 1/500 sec. which most 35mm cameras could not do at the time.
You are probably right. I don't know where I got it (some box lot at an auction, most likely), but it worked in the 635! Lucky for me! I would have hated trying to find the Yashica spool just to complete the kit!