I’ve had to do research in university libraries, Judo 6+dan, direct students of Billy Robinson, talking to people who had access to Tenshin Shinyo Ryu material, bugging people on e-budo, asking for research help from people on the old JudoForum.. Basically, if you want to look into this material, you have a lot of work ahead of you, and you’ll likely never have enough concrete material to publish a history paper on it. Too much is just lost. Sorry to be disappointing.
Do you have some reference to heelhooks in particular being banned? I’m aware of the leglock ban in the early 1900s area but I haven’t seen anything mentioning that Kano’s students were even aware of the heelhook as a technique, let alone felt the need to ban it specifically.
Yeah, my impression is that the heelhook was present in Sambo due to the integration of leglocks from Catch-as-catch-can. I’d love to see some kind of reference to heelhooks in Judo but.... as for now, I’m skeptical.