Mazda B3000 engine swap

Hey, i have a mazda B3000 truck with a 3.0L V6, 154 HP, 180 ft-lb torque, and i was wondering if i wanted to swap the engine to the B4000's 4.0L engine, would it be easy? Considering it's pretty much the same vehicle but with a different engine i'm guessing it'll fit and it should be pretty easy but could you enlighten me?