To switch from rally to Stadium truck, you need upper and lower a-arms, cvds, shocks, wheels and tyres and different clutch bell is advisable although not essential.
When I was running the rally set up, I found the handling to be a little unnerving at higher speeds. Great fun though and the rally bodies look brilliant and offer a little more protection than the truck ones. If this is your second CEN, why not race the other one and just bash this til it needs to be changed and get the truck arms etc then. Just a thought.