Many crashed spitfires ago, I remember talking to Mark at Supermarine, about the problem, we concluded that a couple of small cameras mounted on the spar(s) aimed at the locks would let you know if they were indeed locked.
Seeing the mechanism is bike chain and cable with a gearboxed taper pin at the end it wouldnt hurt..Wasnt there an inflight fix where you went inverted and jiggled the UC selector to move the lock pins while it was unloaded?