Need to be careful shaping that spine on top of what the F-20 already has. That intake at the base of the vertical fin is for a very needed heat exchanger (and the rest of the fairing aft of the air outlet for that contains the hydrazine tank for the remote start capability).
One thing I am tempted to do is replace the single Sidewinder, or equivalent, rail on each wingtip with the double Sidewinder rails used by the F-8. For an air-to-ground loadout, double Zuni launchers on each of those rails.
Speaking of the Crusader's Sidewinder Y-racks, does anyone know where I can find those, in both 1/48 and 1/72 scale?
Oh, a couple other ideas for point-defense loadouts for the F-20. A Norwegian one with IRIS-T missiles on the wingtips and Meteor missiles under the wings and a Japanese one with AAM-5's on the wingtips and AAM-4s under the wings. For both figure an under-fuselage drop tank unless a decent set of conformal tanks could be worked up (given the structure of the F-5/F-20, not sure that's all that feasible, but 'twould look good).