This month in 1957 saw the little Bedford CA van in St John's Ambulance guise. A common sight at the Hertfordshire Show that I used to go to with my dad (and, no doubt at all sorts of other public events across the country).
In cream with the St John's Ambulance motif, this stayed around until some time in 1960 when it was updated to the single screen casting but retained the same catalogue number. The single screen versions are hard to find, not least because many seller advertise the model just from one side!
412 has an opaque section for windows at the sides and rear. I believe it can be found with both types of grille - the rounded top shown in the image above, as well as a distinctly straighter top edge (although that edition I have yet to obtain).
I am not sure that there will be twin screen editions with fixed shaped wheels and they are likely to be pretty scarce on the single screen edition too.