this is how i would go if i wanted to keep it semi cop proof.
YT 1.95 RR (mace ones are 1.98), cai, cat back exhaust (extractors will make it loud), and a little cam with the related gear (springs, timing chain etc...), diff gears and a tune.
As for cops hassling you. There is a 18yr old p plater around here driving a brand new HSV Clubby, i got no idea how he afforded or how he dosent get pulled up. and there are a couple p platers here that drive turboed skyline and xr6t and they just dont have the p plate on. Also my car never used to have mufflers, i have twin 2.5 exh with hiflow cats and only had hotdogs where rear res is supposed to be and you can hear my blower a mile away even wen idling and they never said boo, even wen i would stop for RBT, I even had them pop the bonnet 1 day and i dont have a lid on my airbox. All the copper asked was if i had a blue plate for the supercharger but wen i told him it come from factory with it he closed bonnet and said have a gd day son.
If you drive responsably they wont hassle you. You drive like a dick and draw attention to yourself and they will annoy you no matter wat you drive!!!!!!!!!!!!
well that my 2 cents anyway