Just joined your forum today. Very interesting this ambulance.
One of the reasons for using a panel van instead of a station sedan is because with a panel van body, you can access the spare tyre without interupting the rear load.
With the special purpose of an ambulance and the way it is fitted out, it is not practical to unload the patient on the side of the road to fix the tyre. Further more the floor will have been fitted out differently for the stretcher.
Also the reason why the third door is behind the driver and not the pasenger side as is normal practice for a three door wagon, is because you can fold the front seat forward and place the patient along side the attendant and the driver. If you had the attendant on the other side this would not be possible. FC panel vans and wagons are not really long enough without doing this for a tall patient, trolley etc.
Hope this helps.
Darren Johnston