Hi Graham, welcome to APUG.
There is no single definitive source, although I've managed to cobble together lots of info on the 645 Super, Pro and Pro Tl.
The problem you are experiencing with the grips is what led me, at one time to having three separate bodies - two Super and one Pro.
In essence, the grips were initially made in three sizes for the Super, and they all came with the appropriate connector for the Super - the Connector "N".
Then Mamiya brought out the 645 Pro, which requires a different connector - the RA401. In order to encourage people to upgrade, they sold the RA401 connector separately. They also sold a new grip - The GL401, which came with a RA401.
Then Mamiya brought out the 645 Pro Tl, which added TTl flash capability. And guess what, a new grip (the GL402) and connector (RA402) as well.
The RA402 apparently is compatible with the 645 Pro and GL401 as well.
However, to the best of my knowledge, Mamiya never marketed the connector N separately. I sold mine when I sold one of my Super bodies with its grip.
The difference between the connectors for the Super and the Pro is entirely physical - the camera bodies are shaped slightly different where the connectors connect.
There is no mechanical cable release socket on the Super, but:
1) the connector N provides one; and
2) there are a couple of cable release adapters that have been sold by Mamiya over time which work on both the Super and the Pro and Pro Tl. One of those two accessories locks to the cameras better than its predecessor and/or routes the cable release in a better way.
Some of the camera manuals contain information about accessories, but unfortunately the Super manual isn't one of them.
There is, however a "Quick Setup" guide for the Super
Mike Butkus' site has numerous helpful documents. Here are links to two of them:
1) an accessory brochure which must have come out when the 645 Pro was new: http://www.cameramanuals.org/mamiya_...ccessories.pdf ; and
2) this is the Quick Setup Guide for the Super: http://www.cameramanuals.org/mamiya_...uick_setup.pdf
Mike has a couple of pages on his site that collect links to Mamiya cameras. They are two of my most used bookmarks. Here they are:
Mamiya Camera Instruction Manuals: http://www.butkus.org/chinon/mamiya.htm and
Mamiya Lenses and Accessories: http://www.butkus.org/chinon/mamiya/...ccessories.htm
As always I recommend sending Mike his requested donation(s).
Now I have given up all my secrets! How am I going to maintain my APUG Mamiya 645 and RB67 reputation now?