Different ram pin alignment and other things of that nature. Iirc the g7/fly style volt has the pin about 3/4 of an inch in from the back. The a1 and a1 fly have the bolt pin abou 1/4 of an inch from the bottom, if not less.
The g7 bolt is longer than the A1 bolt. the exhaust hole is also oriented differently. A1 is horizontal to the bolt and G7 is in-line with the bolt. The A1 bolt's pin is a little bit more forward than the G7 bolt.