Where do I start? Well an XR6 EEC-4 will give you a 5800 Rev limiter, better shift pattern along with fuel and ignition mapping to suit the XR6 engine while the Police EEC-4 will also give you an improved shift pattern with the added bonus of no speed limiter and six grand rev limiter (im not sure about fuel and ignition mapping) but it was never released as a XR6 Police pack in EEC-4 form so performance may vary.
(For those that may be confused an XR6 engine only differs from standard by the improved head casting and valve train, namely the valve springs,(larger valves on EF up models) XR6 cam, higher presure fuel regulator 270 to 300 kpa, red rocker cover, XR6 mapped EEC and XR Exhaust system (Twin system on early XR's) and clutch kit, The rest is all the same.
The only XR'S outside this spec are the 25 EB XR6 SS falcons that were built.)
You can keep your stock EEC as it will run your engine but not to its full potential as its mapping will not take advantage of the cam & head mods nor will it operate the Duel runner manifold.
A simple shift lite kit from Jaycar Electronics can be employed for this duty, the manifold (butterfly) standard changeover point is at 3800 RPM but with the advantage of adjustability you could choose the suitable point yourself on a dyno!
The other posibility is to fit an EL XR6 EEC-V (in stock xr or xr police form) as it will run your thermo fans, Knock sensor and duel runner manifold.
The EEC-V has improved mapping more suitable to the EF/EL head and cam, increased memory & proccesing capabilitys along with the extra functions.
Im currently running an EL XR6 EEC-V unit on my EB 4.0 with EL XR head,duel runner manifold (yes it fits!), Knock sensor and thermo fans with the only problem at the moment being an incorrect trip computer reading and a odd fuel consumption pattern that is more than likely my driving ( I DRIVE IT LIKE I STOLE IT!), it will do 100 KM without moving of full if I take it easy and drink a quarter of a tank in 50 KM if I push it!.
Im running an EF/EL 3:45 4 pinion lsd Diff (it has bigger brakes) and V8 gearbox with the GT fine spline input shaft ( the same ratios as th EB XR6 SS used) This is the setup to have!
The EEC-V will Plug straight in and should run (providing you have Smartlock otherwise there are more mods) but Im not sure if it will run the auto correctly as this is something I havnt personaly tried although the wiring diagrams seem to match.
If you want details and pics EEC numbers and availability just post your email address and ill pass it on to you, Its not hard to do, and easyer if its a 5 spd manual.