Hi Richard
Sorry for the delay in responding, all work and no play at the moment. The picture in the drivers handbook shows a rear view of a cabless ( but with floor,engine cover and front panel) two axle Matador, with the 4 batteries mounted transversely across the chassis just to the rear of the cab, in a fairly substantial box. I presumed that this was a temp. assembly prior to fitting the cab and body. The batteries appear to end up fitted under the front row of seats in the body. ie under the gunners seats.
Sadly this won't help you. I can't find any pictures or references to batteries on the 3axle chassis, and I don't think the box you have beside the fuel tank is big enough for the batteries. In the picture I have, the battery box is almost the full width of the chassis at the rear of the cab.
Steve