The proposed brake horsepower and torque wont add much performance if its lugging a landy chassis around . The side rail height is such that it would greatly limit your ability to lower , if you want to get an axle under it .
You need something with a thick and narrow (shallow) chassis rail , so that you can have a kick up at rear to get the axle in . If you look at a standard landrover it only has about 4" between the frontaxle and bump stop , and thats sitting on 16" wheels . The only other way would be to use traingular arms top and bottom with the inner ends located at bottom edge and top edge of landrover side rail . Space frame will be far more effective , Colin Chapman of lotus used lightness rather than more power to achieve success . If you are intent on sticking with a landrover , then start looking at gas turbine engines to get enough power , as i/c engines you will end up with something the size of a steam foden