I've seen a few, and they don't look like the line up centrally with the reg plate, slightly to one side.

This is not the centre exit one. This exhaust is the one that has a 140mm X 70mm pipe each side just below the black plastic grill in the bumper.

Or did you mean that the reg plate doesn't look in the middle of the two exits - sorry didn't read you post right.

Your reg plate WILL be dead central with the car, these Duplex systems from Peco appear (once fitted) to be slightly off centre to one side, it is noticable when you look at the reg plate alignment and compare it to the fitting.

for the right side there is no rubber hanger. you should have a big bracket that comes off the pipe, which screws on to the bracket that is in the boot floor, neer the back of the bumper

i will get pictures.