OK Guys(and gals). I'm after information again, having spent nearly two hours on Google etc.
According to 'Wheels & Tracks- Historic Military Vehicles Directory' 400 of these trucks were supplied to the UK, originally as artillery prime movers ( alternative to Matador - medium artillery tractor?).
I would like to make my forthcoming project as one of these trucks and need a picture or two, or maybe just unit info so that I can trace markings etc. for the model.

this thread at Maple Leaf up forum may help.
http://www.mapleleafup.org/forums/showthread.php?s=f725118251454727ec357eb36110099e&threadid=1785

Thanks Roo, I completely forgot about Dave Haywood & Hanno - should have thought about them and asked........ Dave has more stuff on allied trucks than anyone else I know. You may be interested to know that last time I spoke to him he was writing a book on CMPs.

I have ordered one but have not heard back from him.

Great info. from that link.
65th A/T Regt. 7th Armoured Div. used them for 6pdr & 17pdr prime movers; Italian campaign & NW Europe. No census numbers but at least it'll have formation & unit signs.
There doesn't seem to be any hard info. on the quantity of the 400 supplied that had hard or open cabs, but a lot of the later ones would probably had open, and that's what's in the Heller kit so..............