IIRC, the left hand grips for the older and newer style Mamiya 645 cameras cameras can be modified to work on the cameras they were not designed for. Generally, the only modifications necessary are to the part of the mechanism that contacts the shutter release on the camera.
This very left handed photographer finds the left hand grips to be extremely useful on each of the Mamiya C330, Mamiya C220, Mamiya 645 Super, the Mamiya 645 Pro and the Mamiya RB67 (in order of acquisition).
When I was using the (now sold) Mamiya 645 Super, I had both the correct grip for that, and a grip for the older Mamiya 645 series. I could made the old grip work with the Super.