I photographed these Dodge WC54 Ambulance examples at Arlington, Hill AFB, FHC and IWM Duxford
One of the visual differences between the WC54 and the Dodge M43 Ambulance is the bulge in the roofline, especially when seen over the rear doors. The M43 also is slab sided, while the WC54 has a ridge of bracing above the rear tires.
The Dodge WC54 Ambulance is a 3/4-ton vehicle, while the Dodge WC9 Ambulance is a 1/2-ton vehicle. Look for the vertical louvres on the WC9, while the beefier WC54 has horizontal slots.