I have two UK Government surplus cash boxes, nothing really heavy duty, they would have just held an office petty cash float, although they are better quality than what you would normally buy. One I have a key for, but I've lost the key for the other one and it's locked

The lock is a small snap type 5 lever lock made by Yale (On the back of the one I have key for it's stamped "YKB xxxx" with xxxx being the key number. The key is completely flat about 1mm think so quite simple to make. Anyone know of an NDE technique for this lock? Once it's open I can make a new key for it. Looking at the box that I have a key for I've figured out two minimal damage ways of opening it by either drilling a small hole to insert a wire to push the latch back, or drill the four spot welds holding the lock in place, I could then repair the damage but I'd like to try an NDE method first.
Martin.