The muffler shop you went to are idiots. First things first, are you running a header? If not, get one first.
If you are running a header than any competent muffler shop can run the pipe at the width you want and stick new hangers in where needed.
I you're not running a header then they would have to use your old factory exhaust as a flange because of the oddbal outlet on the stock manifold and then they could step up to the size you want, but it's practically pointless unless all you're doing is changing the pitch.
For the muffler, it will fit in the stock location and you can run chrome tips out. Otherwise it will require making space somewhere under the car and a whole lot of fab work to get the dual pipes to fit around the suspension and out where you want it. Stick it in the stock spot and run tips, it's easier.