Rusty,

My oil cooler "diffuser" is almost identical to yours except mine tapers to zero distance from core at back end.  Extensive wind tunnel tests (squirting compressed air nozzle at inlet and feeling where air came out of oil cooler) showed that most of it was at the back end (no big surprise).   Already been some better permanent solutions suggested here but as a quick fix I put a piece of ridge vent material (very porous fiber stuff used to vent roofs) at the back end to equalize the flow through the core.  Not a great solution but did show measurable improvement.

 

Your installation is really looking pretty good in the picture you posted.  Only thing I would suggest is to carefully measure the pressure drop through the scat duct to throttle body.   Possibly even worse than the pressure drop is the heat the air picks up going through that thing (at least that's my theory).  I was flabbergasted at the improvement I got when I eliminated the scat.  Mine was a bit longer than yours so the penalty may not be that much in your installation.  Worth keeping in mind though.

 

Tracy  (suffering flying withdrawal, runway predicted to be dry enough for takeoff by fly-in time next weekend)