Re: F150 (2004+) cummins swap?
If you go diesel you'll have to go with hydroboost brakes.
Why not use a Cummins 4BT3.9?
It's two thirds of a 12-valve. It can make an honest 225 HP all day long. 300 HP for short bursts. It's lighter than a six and shorter to boot.
I recommend you also go with a stick if you can handle all the hassle of an engine swap. Diesels eat automatics.
2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Rugged Air Dam