Fi would make it more fuel efficiant. The Magnum 3.9 has more Hp too. It wont be that hard if he can find a whole truck for the swap, than he would have all engine related parts. "IF" he does move forward on the swap we will have to look further into the centerlink. What els had the 3.9 other than the Dakota, Full size trucks and Vans? Might be able to mount it back enough to clear? I havent really look at the car to even get a feel for what would have to be done. Plus using a 3.9 if he decided to rebuild for power reasons it has the same cylinder bore as a 318 and he could get some good used higher comp pistons or if money is available a supercharger (procharger) or turbo it. Remember thier will be a bit of room front and back of the motor since it is shorter buy 3 cylinders