I know that pic is in Ryton's Book Schutzenpanzer; I'm not sure in wich book I have take mine; maybe one of this 2:
Schutzenpanzer (part 2) - Tornado, Tanks on the Battlefield 4
or
Sd.Kfz.251 Hanomag (part 2) er...I don't know the Editor, but the serie is Military Machines 103 (or MIlitary vehicles 103, depending of the translator you use
)
I scrachtbuilt 4 ammo boxes using the Italeri 10/4 as guide. You can see the finished model here:
viewtopic.php?f=18&t=438Cheers
Darío