4.2s are great.... in smaller cars with manual trannys..... and the 5.4 isn't a 351 its actually a 330CI motor.... it almost resembles an older Y-block..... getting the 4.6 and 5.4 in are going to be exactly the same trouble, they're both the same block, they just have a different stroke and different heads.... now... if you're going to go with the 5.4 i reccomend 03 and up... because they changed over to that 3 valve setup in the heads.... added some extra power to the motor for really no cost on gas mileage at all..... for changing out the engine you're going to have to get the motor, a wiring harness for your year truck with that motor, the radiator for the motor, the ECU, and make sure to take the clutch with the flywheel..... but thats where your largest problem is going to be.... finding a 5.4 truck that has a stick.... almost all of them are autos, unless you goto the f-250 superduty...... even though i'm sure you can probably buy a new flywheel for the motor, might even be able to get a lighter than stock flywheel.... other than that its not going to be too rough.... goodluck