Okay the 4.2 is a stroked 3.8 .. u can get a good one out a junk yard out a f150 on a stock basis it give u 50+ HP over the 3.8 stang engine.. will drop right in ur stang fine.. Ull want a 01 + truck engine tho..
And u can go badass and get forged internals or keep it easy both works
Windstar upper will fit right in there on the 4.2 as well
Ull need to reuse your stock cam position sensor
Oil pick-up tube and screen
Ur 3.8 damper
3.8 oil pressure sender and tube
How to: 4.2L V6 Mustang Engine Swap