Don't be confused: you're right, you have a SIII. Not only by the dash, but if you look at where the windscreen hinges are, it's the squared tower (SIII-only), all IIa's had a vertical plate, and Defenders have ones that bolt onto the windscreen and the bulkhead directly, w/o the tower. That's the easiest way to tell from the outside, because all the other bits are interchangable (wings, grille, bonnets, etc.). It's easy to make a III (superficially) look like a Defender, or a IIa, but those hinge mounts are pretty much fixed w/o a LOT more work....
-L
'72 SIII SW 88"
'60 SII 88" RHD