Oh. I had not gotten the idea of the transverse supports placed in front. Thought it was nearer to the rear axle, where the body can be anchored to both the framerails in parallel and get supported by the suspension/frame complex.
I now understand your concerns, and I agree with you. If the body is fixed transversally to the frame in the front, near the cabin, where this has no big support or at least not the support or structural strenght given by the mentioned complex, you will have a lot of twist allowed by the longitudinal aft supports, that will keep the static and dynamic fro-aft weight in order, but the dynamic force when cornering or ditch crossing will pull the frame from the front, from the armpits, for to say, and it will twist a lot.
The three-point system, front or rear two fixed transversal points, works beatifully with short bodies, but yours is long.
The body is very well constructed, pretty tough... and heavy. Long as it is, with such arrangement there will be a lot of mass and torsional stress along the body itself taking the force from the rear the middle and the front sections to the supports in the front. A diamond shaped system would distribute the weight and dynamic forces more even.
My truck is having such an arrangement, with only four points.
Just in my humble and poor opinion.