I didn't know where to put this but I will give it a shot here.
Try
www.webkits.com.br for a real trip.
It is a Brazilian modellers site and the language is Portuguese but it is manageable.
Hit the tab "artigos" then the tab "tecnicos"
This brings you to their model review site and more. Of particular interest to me were two threads on American Staff cars and not less than six threads on German staff cars
These are extensively documented and do not deal with models per se but are full of info and photos.
Then, there are over 100 model reviews, including many vehicles discussed here, with period photos and exhaustive step by step modelling instructions.
I will try to communicate with the webmaster in my very rusty Spanish and see if they intend to do more on staff cars, particularly British ones.
Bill