I'll have a go at answering this...
First of all, then head will have oval shaped intake ports. It'll also have double valve springs and larger intake and exhaust valves.
Intake: 35mm (optional 37mm)
Exhaust: 29mm (optional 30mm)

That's the head covered.
I think most (if not all) GX models came with a dual carbie setup as well.
Look for GX badges on the exterior if they haven't taken off already.