Hate to say, but to me it looks like someone's been "at it"
Rear tub is civillian front fill 2a, mil fills under the seats, front wings are 68-71 2a, front panel is 3 (unless the hooks and holes are there for the cross-type 68-71 2a wire grill), 3 bulkhead, 3 deluxe bonnet (optional extra on 2a), rear spring hangers and front dumb irons look extended from photos so could well be an ex-mil chassis.
Any evidence of the ambulance front and rear anti-roll bar mounts on the axles or the chassis? Are the axles reinforced mil Rover 9/Rover 11 front and rear, or has it a 3 salisbury rear? Are all the ancillary outriggers on the chassis for twin tanks etc? Do you have a mil square rear xmember or a tapered civvy one? Thick or thin rad? Thick for '64.
Etc etc, nice truck, COUGH.... ditch the ambu plate and get a plain one stamped up...... COUGH
What military reg number is on the plate by the way?
Alec