Bafang Models confusion for Mid-drive compatability

[mike_kelly]

I am interested in building up a carbon mid-drive. Unlike many I am not interested in speed at all. I am interested in climbing and lightweight. It seems that commonly available frames are specifically made for the Bafang M600. It also appears that the M500 is also compatible with the M600 profile. But what about the other motors in the same family like the M400 or the M510? Is there some spec that clues you into what motors fit in a M600 frame?
Also I see M600 referred to with a G number like "M600 G510" but I don't see the G numbers in any of Bafang's catalogs just the M number. It is too hard to find these to make a mistake and end up with a pile of parts that don't work.
Thanks for any light you can shed.

 

[AHicks]

That's the downside to the M600. The special frames you need are hard to find.

 

[mike_kelly]

The frames are easy to find it is the motors that are hard to find.