Exactly what the guy with the really long screen name said. As long as the motor is the same year as the vehicle or newer, from the same manufacturer, and all the emissions equipment is intact, you are good to go!!

Although, there is always option B (the one that I use). Make sure that your rents stay living in a non-emissions controlled county. So when you have to move to an emissions controlled county you can just keep the truck registered with them. Heck even my insurance claims that my rig lives 50 miles from me and is only driven by me 10% of the time.