Juergen Mattern (1944-1995) earned this game essentially by becoming 1975 European champion as 6-dan. Kido arranged the game and gave each side a generous two and a half hours.

Some questions arise. How does 6-dan amateur then compare to now? Mattern improved to being able to take two stones sometimes, but Takagi also improved and became 9-dan. Did he improve more than Mattern?

But most interesting of all - did Takagi arrange the jigo?

m12 looks more like 16k than 6d

To me it looks more like an impatient move, which is what indicates to me most he isn't strong as average 6d these day. It's not kind of move you'd normally see in 6d game, and esp. in handicap game and special game against professional. However, he could have just been very nervous. Maybe 6d, but not yet mature personality. Also, he puts himself into poor fight often; and I don't know any 6d that would play r16. Maybe he is 3d, however I'm not very good at judging rank. Just my 2cents : )