Looking at the condition of the vehicle it came out of, it had probably had previously gone through the Tenix rebuild program. But without the Service Record Book, there's no telling the reason why the Ambulance was reduced to parts (missing G/Box might be a clue, or a red herring). Without knowing why the vehicles were taken out of service (perhaps a blown gearbox, who knows?), there is simply nothing in any way, shape, or form to suggest or rule out engine failure. Compare the cut Heater hoses to see what engine came out of which Ambo. I think this parting out was more likely done by AFM rather than the Army.
One of the 2 in the last auction had a stuffed crankshaft (spun bearing) and there was also nothing to suggest there was anything wrong with it either. It turned over ok but the problem surfaced when it was started. As I said possibly there is nothing wrong with them but just as possible they could have been hydrauliced or cooked and you wouldn't know until you tried to start it. That's the gamble you take if you buy a condition unknown engine - buyer beware and bid accordingly. You might get a bargain but just as likely it could be a lemon.