Would be very unlikely to be a B06, XU4, M21. Most Ambulance packs were autos. I have seen in my life as a Holden fan only one genuine 4spd B06, and it was a HZ 1-tonner, L32 M20 in Panama Green. Most BO6 vans I find ae 14.5cwt as the Ambulance gear and passengrs weighed more than 10cwt (500kg).