Top guns fitted to early marks. You could also fit a gun pack instead of the missile pack and get 4 Aden cannon on board!! Great fun to fire but the vibration could cause problems!
A similar fun shoot was multiple SNEB pods, using the 116s that were supposed to jettison automatically when fired out. I've done it with 4 pods, flying out of a field site in Germany. The take-off calculation was interesting with big trees at the end of the strip, and 1 of the 4 jets had an outboard hangup that he had to bring back for a VL.
I also saw the aftermath of perhaps the only Harrier 6-pod shoot (using twin-store carriers), which showed that there was a high probability of self damage with so much debris flying about, especially the frangible nose cones.