98 f150 motor swap

Biggest thing is the computer, it needs to be flashed for factory specs (engine, trans, rear diff.), as well as vin and anti-theft. It involves a lot more than just the engine. Most of the big ford forums have guides of people making such swaps.

Your wiring harness needs to be swapped, headers, trans will also need to be swapped (4r100e in v6 applications, 4r70e in v8) as well as drive shaft, coolant and power steering components, heads, fuel pump, and fuel rails. It's a headache honestly. Just put the same V6 in and sell it to buy a v8 model