If you're swapping a complete engine, with EFI, sensors and such, it's almost a bolt-in. Swap motor mounts, swap engine, plug engine harness into body harness, swap EEC's from 302 to 351W.

All junkyard or ebay items.

The thing to pay attention to is if your truck is mass air, then you need to swap in a mass air 351W for minimal hassles. If your truck is speed density, then a 351W speed density EFI setup makes it easier.

It's when you cross from one to the other, that you have some wiring and sensor changes to make. All doable of course, just takes more time and a bit more effort in getting things right the first time.