VX275 is spot on.
the envelope based on two Landrovers side by side was cast in 1995. At the time the spare wheels were being strapped on the side of the landrover not on the bonnet. necessitating widening the fuselage by around 6" (150mm in metric) from that proposed by Airbus.
The spec for the loads was referred to as Exhibit A. I never saw it updated in 10 years. the copy I held was an A5 spiral bound booklet about 1 1/2" thick.
I know Airbus struggled to keep the weight within that predicted. Growth ate into payload.
I lost touch with the detail two years ago but I know the team at ABW worked hard to get the best deal for UK. I don't remember ever seeing some of the bomb proof vehicles being used in Afg ever getting into the Exhibit A. Particularly the SUPACAT HMT variants. (Jackal) I know the French and Germans had a big six wheeler similar to the Saracen which was driving the design.
I am sure the highly professional guys at JATE would not exceed the agreed floor loadings. I understand they have been working closely with Airbus in Bremen. I think they would have the rear cabin mock up at Brize by now to be developing all the load plans.
Folks do realise that the flat floor is only 1/2 a yard longer than that of a stretched Herc. but you can get a SWB landrover on the ramp. It's great to have the width to walk around stuff though.