I need a rear end

Any salvage yard will have what you need, tons of Crown Vics at these places. Take a copy of your VIN, door tag info as well as numbers on the metal tag attached to rear axle if you want to find an exact match. 03 thru 07 are all same generation so all rear ends will fit.

PS forgot to add: pay attention to what size rear rotors you have, they did switch from 16" to 17" somewhere in mid 2000s, at least on the police interceptors.

03-11 will work. they changed to 31 spline but the whole assy swap will work