Paul,

If you want to consider a plenum, I suggest you get in contact with Clark Baker.

He has a really fast Legacy with a plenum.  He could probably send you some pictures of his install

D Brunner

Tom: the sides are well defined and the rear has angles already built in.  I can tell from the rubbing marks I still have lots of leaks in the rear area.  I'd rather put new effort into a plenum instead of silicone baffling.   I think it would still be a net positive despite leaving the inlets alone for now.  Maybe it will become apparent when I start to plan it out.