Is it even possible ? If so, can someone point me in the direction of the required adapter ? I'm curious if the new 120 pc-ts apo macro Schneider could be used on a Hy6 body ...
It is possible. However, due to in part that it means using 645 lens on 6x6 camera and simply because mounting flange for lens is shorter distance to sensor plane for Mamiya 645 it is only possible to use for very near focus (macro). One could thus make ones adapter by demounting a flange from a Rollei extension tube and screwing with screws together with a flange from an old Mamiya lens (it may need some shim also).
Acutally I tried by simply holding the Mamiya 80/1.9 in front of my Hy6. Near focus of course, and per memory in the range of 20-30cm or so. Is it worth the effort? I purchased 9+17 ET instead for use with the Rollei 80mm and which shortens nearest focus and thus gives suffice shallow DOF for my needs.

For T/S, likely not worth the effort to mount a Mamiya on Rollei. I did see a Rollei T/S on Ebay the other month so they do show up. Per memory it sold for roughly around 5,000 USD and was one of those few Rollei items on Ebay that sold very fast.
Regards
Anders