Mike,

Beware. The motion of the engine relative to the body is extreme. Probably
centimeters in amplitude. I would still mount the muffler (both sides) with 1
inch thick super heavy duty truck muffler hangers to the engine mounts and
oil pan end. I used a vertical hanging approach with 0.75 inch Al plate to
bolt to the engine. Then use a flexible bellows between the collector
junction and the input to the muffler or CAT, whichever is first in line.

Of course advice is cheap, but your under the thing. Don't be afraid to throw
in some bends to get more length! Of course, I don't have a clue about the
plumbing of the Subaru exhaust!!!

Let me know how you fare.

Frank Grunthaner