Are the single cat and dual cat stock exhaust manifolds the same? If not, can anyone point out the physical dimensional differences or have a side by side picture?

 

The dimensions are the same, but the connections are not the same. The AIR connection is 22mm on the single-cat and 18mm on the dual-cat. The driver's side dual-cat manifold has an oddball triangular flange on the end, that the cat bolts to. The single-cat header does not have that flange.