I use Pocket Wizard with my Bowens flashes, and Nikon digital and analog bodies and Hasselblad, it has worked flawlessly for me, I’ve also used it for triggering a hotshoe flash (Nikon SB-800), all good. I presume the 645 has a hotshoe on it, so, the sending unit will work with no other cables, otherwise you plug in a sync cable between the camera and radio which is supplied. Same on the flash side, one of my Bowens has a built-in PW radio card, so I usually set up to trigger it from the camera.
Pocket Wizard does have support for some TTL systems, though not sure if that includes anything Mamiya has, but you need a compatible flash too.