Security - If you are changing the locks you will need the main ECU, the keyfobs and tiny transducer chips from them and the immobiliser module from the steering column. They all must match!
Sorry to be blunt but this type of question baffles me because it is so senseless. Whatever happened to the old 'if it ain't broke, don't fix it' ideal?
Where do people get the idea from that ex police vehicles are somehow far superior in performance; Its ridiculous. They are trained to be far better drivers and are taught many skills in that arena though.
As for the Omegas they used, and maybe some are still in use, they were/are the bog standard V6 3.0 litre, 5 speed manual saloon and estates. The only differences are that the suspension was uprated to cope with the heavier loads of the masses of equipment thay had to carry 24/7, they tended to be manual 5 speed boxed, some tended to have a modified differential to aid with acceleration which gave them blistering 0-60 times but at the cost of a big drop in top speed (the type used depended on its role in the force) and they also had a larger alternator and a suplementary heating system. The faster acceleration model also suffered greatly reduced mpg too.
Being ex plod they also have a lot more holes, which with luck will have been sealed and grommetted, and some extranaeous redundant wiring from their gadgets. Take also into consideration that they are thrashed during their working life!
What is wrong with the power you have as standard if it is properly maintained and set up? Are you a boy racer wannabe or something?
Best advice is to leave it be, all the advice you have had from everyone is correct!
There is a commercially available chip, sold on Ebay which you can fit at your own risk that will enhance bhp to some degree. I will not list the seller so please do not ask. Boy racers buy them. Quite why this is needed in a high power lump to begin with defies logic and all common sense!
I suppose that you will disregard all sound advice and go for it anyway. I, pretty much like the others I think, hope your driving ability will be up to the standard required to ensure the safety of all others while you are demonstrating your 'skill'. Just make certain it stays as 'skill' and not the shortened version 'kill'.
Final point - don't forget to tell your insurance so they can sting you for a hell of a lot more, and void it should you opt not to inform them and are subsequently caught out.
GudLuk, you will probably need it.