Nearly there Don: the GR5 was supposed to get the new 25mm Aden, but never did.
So,
Point 1 - correct
Point 2 - never got the gun
Point 3 - correct
There is a family tree here that may assist:
Harrier GR1, GR3 and Sea Harrier - all-British design, traditional airframe construction, 30mm Aden (that worked!). Also entered service with USMC as AV-8A.
GR5, '7 and '9 - BAe/McDonnell Douglas co-production (entered service with USMC as AV-8B Harrier II, and later Spain & Italy); bigger wing, parts composite construction. Each nation specified its own armament: that in the AV-8B family worked - that developed for the GR5 didn't, and was never fitted (though the a/c were built with the pods to take it when it became ready). One or two may have flown with the 25mm ADEN pods for trials purposes, but it never entered squadron service.
The GR7/7A and GR9 (and now the Gr9A with an uprated engine for service in Afghanistan) are just re-engined versions of the original GR5 with updated EW gear and weaponry options etc.
All GR5 airframes were converted to GR7, and later GR9 standard.
For more details of all variants (but lacking armament options, alas) you may look here:
http://www.harrier.org.uk/history/hi...production.htm