The hitch I have is only as wide as the frame rails and the exhaust pipe runs outboard of the frame rail, so there should be no interference. I only have a single exhaust but looking at the undercarriage pics at:
Ford Crown Victoria Undercar Picture Scrapbook
it looks like the same for the PI duals. As long as the overall width of the hitch isn't much more than the frame, you will be fine.
A 2" receiver is handier if you want to use an add-on cargo carrier,bike rack,etc. because most are for a 2" tube. You can get an adapter but the weight capacity is lower. I use an adapter and a front wheel hitch to tow a motorcycle occasionally.