usually when the cab and i believe the engine as well is raised higher is to facillate the driveshaft to the front wheels to make it an all wheel drive truck for extra grip and traction
so the picture u have of the real truck with the raised cab maybe have 6 wheel drive
so if u want to build similar, i suggest raise the engine up the same height as u raised the cab and scratchbiuld the forward drive shafe and axle