I am "in the process" (been so for more than 2 years now...) of swapping a 351W into my 1999 4x4. I had to make a custom oil pan to fit the 351W into my truck. But I have a 4x4, so was a little tighter than some. Over on RPS, tony is also doing a 351W swap in his 2000. I can't remember for sure, but I think he is using a mustang pan.
Toughest part will be exhaust. I had to make custom headers for mine. To get big power and move the air of a 351 or bigger, you really need to anyhow.
Check with tony and see what he is doing for the pan and headers. It has been a long time since I have discussed this with him.
DD: 2010 Sport Trac Adrenalin. 4.6L V8 / AWD with Terra Grapplers and Voxx G-FX wheels.
Toy: 1999 Ranger 4x4 4Door. Replacing 302w 1.5L Kenne Bell with a 351W: Explorer EEC-V DIS, AFR205 heads, custom 1 3/4" long tube headers and Autorotor 2.6L supercharger, intercooled with '03 Cobra and custom fabricated manifold.