I looked into the power chip about a year ago and each maker can tell you what will fit were. With powerchip they claim that they will program the chip with the information you give them about you car (if it's stock or you made mod's).
Personal I gave up this line of power has it seems some people say it has improved the work and others say its a waste of time and it's a lot of money just to see who was right.
I'm currently looking at a Real Time logger for the EEC IV so I can see what the car is doing (Oxygen levels, temp volt's, MAF etc etc) to mod the computer myself (or with the help of someone that knows what they are doing). But this alone can end up setting you back upto $1500. But a lot of guys from the US have had success with them on the 5 ltr. (This in mind I don't know if they work with the 4 ltr)
NC Fairlane 5Ltr Twin Stainless Steel 2.5", Air Induction