WEBF- The cannon pods on the SHAR will not fit on any Harrier II fuselage.
The 25mm twin Aden set up trialled on the GR.5 had a nasty habit of discharging links onto the carbon tailplane and with other problems it was swiftly forgotten about. Buying the American GAU single gun would have been far easier. However with operating 'hot and high' and shipborne the weight of gun pods is not something you want to be a carting around .
As for your comments NURSE - we I guess are alone in retiring our shipborne dedicated air defence aircraft - we are either very savvy or prepared to gamble!