Originally Posted by jgrimm

If you must have a 5.4, Id go with the 4V out of the 1999+ Navi. They are numerous and availible for around 1500-2k at local junkyards. Here's the FAQ on it:
5.4L DOHC Swap FAQ's by Grimm

The stock computer should work fine.

The intake is def. not 1500$ Sullivan makes a nice intake for around 650 bucks if memory serves me right. HPS also makes them. The Sullivan will fit under your stock hood.

If you are concerned about weight and still want a 4v engine, go with an Italian block (Teksid Block) 4.6 4V out of a Mark VIII. Its cheaper and lighter than a termi block and can handle 1000+HP easy if you put a forged rotating assembly in it. If its the bigger size you want, there are a few companies that sell a forged stroker kit for around 1k minus pistons (this way you choose the overbore). This is a good choice if you wanna boost it later on down the road and the Mark VIII's powerplant isn't slow in stock form either coming in with 290 Stock HP.

Also, if you go to your local u-pull-it or pull-a-part yard, you may luck out on a Teksid block 4.6 as the engines are sold at a flat-rate. (About 200$)

The 5.4L 2V only weighs 25LB more than your stock 4.6L. Its the same block.
Mod engine weights in LBS:

4.6L SOHC 500 lbs.
5.4L SOHC 525 lbs
4.6L DOHC Aluminum Block 425 lbs
5.4L DOHC 540 lbs
6.8L SOHC V-10 640 lbs.

The stock strut tower bar should work, but I would measure to make sure.

Exhaust-wise, you will probably have to use a shorty header as you have less clearance due to the wider stance of the engine. I know the 5.4 4V is 28 1/4" wide as opposed to the 4.6 4V's stance of 26 5/8"

You wont have to do much rigging. And if you keep the emissions equipment in tact and hooked up, you'll pass...

-Grimm

Originally Posted by mark a rittenhouse

incorrect. MHS makes a very nice intake for the 5.4 for about 600-800 bucks. its a dyno proven 15-20~rwhp gain on an otherwise stock motor, not bad for under 800 bucks. i cant remember the last time i spent 800 on a bolton for my car that gave that kind of gain. but MOST people do not have to get a new hood with this intake.

incorrect again. ONE company currently does make longtube headers for the 5.4 swapped mustang and they have been for a while, but they are about 1000$.

Originally Posted by mark a rittenhouse

nobody makes a 5.4 two valve intake that i know of besides logan and reinheart out of canada, i beleive thats how you spell it. Hps might never looked in to it. As far as your 1000.00 headers go, that are suppose to be in production, called that company at least 10 times over a one week period left mess. no one called me back at all not even once.

Originally Posted by MU71L4710N

read 1 and 2 posts below my post on the first page. i fudged the company.