Nothing really. You might need to beef up the axles a little to handle the extra torque, but other than that the 2.5 is still a .15 engine. It just has more power. Kind of like dropping in an OS, Fantom, or some other aftermarket powerhouse.
You will need a bellcrank like FT said or you will have to move your tank and cut the chasis . I wouldn't worry to much about it at the moment because the only place to get 2.5 motors is in a new truck or on e-bay no one has them yet when they were supposed to be out in november. x