laisy said: Don't think so, G3M doesn't have the antenna mast. The cockpit part do look different though.
Here are some things though based on what I see:
1) The G4M has a dorsal turret which sports a 20mm Type 99 cannon that can fire in a 360 degree arc. The dorsal/rear gunner here is manning a 7.7mm Type 92 light machine gun peashooter with a drum magazine and has a 90 degree firing arc only, also G3M dorsal gunners have retractable windows like the one shown in the picture.
2) The G3M has a bit taller and more boxy cockpit window, compared to the more aerodynamic shape of the G4M's cockpit window.
3) Can't say about the antenna mast, sorry.
4) Maybe inaccurate but I wanted assume some mistaken this for the G4M because of the familiar paint job the artist put in. The G3M originally has a brownish colour/army camouflage style while the G4M has the deep green paint like the one you see above.
G4M1. The 7.7mm flexible dorsal gun was replaced with a turreted 20mm and the RDF loop antenna was moved under the nose only from the G4M2 on. G3Ms did not have nose glazing except for several of the prototypes, and the glazing over the cockpit was different (with frames not in a regular grid, unlike the G4M.)