If anyone else needs this information, 'Topper III' was a 'B' model.
I'm building a model of this aircraft and will put it the 332nd Tribtue site if anyone wants to see it.
http://www.blueskygalleries.co.uk/page42.html
There is already a nice selection of 'Red Tail' P-51 models to view if you like this sort of thing.