The machine I have is very similar to that (Tascam 38), although the Teac 80-8 has the advantage of being able to run at the correct speed (7.5ips while the Tascam 38 only runs at 15ips).

From reading the papers published at the time (mid-to-late 60s), it seems the encoding scheme was based off a comb-filter, although I don't honestly understand enough to actually describe how it works.

I've had the tapes for around 5 years now, and managed to do basically nothing. It would be good to finally make some progress! I'll send you an email.