Well yes, it's a good start. I actually posted in another thread, but will copy it here - Marcus' comments are generally correct by the way.
Looking at the CAD drawings the following points stand out as needing attention/adding:
Outboard weapon pylons.
Smoke marker dispensers on rear fuselage
AN/ALE-47 CMDS dispensers on rear fuselage.
FLIR in LH Nose door.
ESM antennae on nose doors and tail.
Different Flotation pack fairing either side of the nose and different MLG Fairings.
Looking at the CAD Drawings, it isn't showing inboard pylons and AUX tanks, but that might just be the drawings as these were even fitted to the Fs.
Decklock
HF Aerial running down LH side of rear fuselage.
Different rear cabin layout and LH cargo door might be different too.
Winch boom on canted bulkhead.
So, quite a bit, but at least you don't need to scratch build the G model engines and main rotor blades like you would if starting with the Matchbox F kit.
Oh yes, and rivets! The Seasprite is covered with raised rivets, they really are quite obvious.