Yes in a way you are correct the Thrust this engine produces can make the car unstable, But let me get it clear that its not just 2jz or 1jz that would make this car unstable its any kind of Engine change, reason being that almost all the 4X4s and SUV have a defined center of gravity which is very important for there ability to stick to the ground and perform. But when tampered with this all the dynamics of the car change and it does not perform or behave in its original way, at this could be very dangerous at times.
My suggestion would be rebuilding the old engine and if some one wants performance get a CAR ...
This is a the main reason i am against engine swaps in SUVS ...