Just buy a Ford Racing PI intake manifold with the Aluminum Crossover. Or look in the classifieds here there are always some for sale, i think MustangChris may even have one
Crown Vics, Mercury Marquis but like said above they didn't swap to PI until after the Mustang so 99-00 and maybe even 01 are still NPI on some of those cars.
They generally sell used for @$100+ ship with aluminum crossover or you can get a new FORD one for @$200 online at American Muscle/Jegs etc
ebay has the best deal, theirs a company that makes the complete kit that has everything that you need, including rtv and orings.. im not sure if they still have it in existance, but i used a kit on mine.. back when lol, and ive used 2 on buddys cars and have everything works out fine, its all oem, and i think it was like 175$ if i remember right shipped.. which is good for all new stuff..
Ford explorers have the PI intake as well I believe. I test drove an '05 explorer a couple days ago with the 4.6 and it had it. I paid $50 for my PI intake with aluminum cross over so don't pay more than $100 for one. All I needed for the swap was the coolant pipe, and PI intake gaskets, and the swap takes under an hour.
No, the first 2 years 99/00 had all plastic intakes and at that time Ford was having issues with the 96-98 and 99-00 having cracks so the aluminum crossover models were basically revised "quick fix" intakes. The 01 -04 had them stock and anyone with a 96-00 who had a broken plastic could get the aluminum for free.