Art,
<<Has anyone done any work with cooling drag.>>
Yes, but on a 360 not the IV.  
The principles are the same but being turbo charged changes your cooling
demands with altitude.  Normally aspirated engines have the advantage of
heat generation falling off with altitude.
Reducing your exit area will reduce your cooling drag.  You will see an
increase in pressure below the engine.  Your CHTs will rise, but you
have margin there.  Reducing exit area doesn't mean just blocking off
the exit, it must be done smoothly otherwise you will reduce airflow by
simply adding losses.  
On my 360 the biggest improvement came with the conversion to a hard
plenum which cut cooling drag in half.  That provided a 5 kts increase
in cruise speed.  While even more speed is possible, I like having low
CHTs.
Chris



Chris Zavatson
N91CZ
360std
www.N91CZ.com