Steve,

The test stand load was a 3 blade Warp Drive HP prop.  The engine-reduction drive assembly was mounted such that it was free to rotate on an axis collinear with the engine eccentric shaft but the rotation was constrained by a load cell.  The load cell measured the torque which, along with the prop RPM, allowed the HP to be calculated.

The prop blast supplied the cooling air to the radiator and oil cooler ducts.  The pressure on each side of the heat exchanger core was measured using piccolo tubes across the core.  The piccolo tube holes were 1/16" dia  at a 1" spacing.  The holes were oriented perpendicular to the air flow through the core.  Each piccolo tube was connected to one side of a differential pressure transducer while the other side of the transducer was open to the atmosphere.  It would have been possible to measure the delta P directly using just one differential pressure transducer for each core, but I was interested in the absolute pressures as well as the delta P.

The same setup was used in the plane to measure the pressure at the inlet side of the core of GM AC evaporator cores used as radiators behind short ducts with stock cowl nostril inlets.  In flight, the pressure at the core face was about 80% of the pressure measured by the airframe pitot tube.  With an in flight pitot pressure of about 10  "H2O, the pressure in front of each radiator core was about 8 "H2O and the pressure inside the upper cowl (not near the radiators or cowl outlet) was about 4 "H2O, all relative to the airframe static source.  During stationary  run up with a prop RPM of 2400, the pressure recovered at the left radiator core was about 1.8 "H2O while the pressure at the right radiator core was about 1.5 "H2O.  Overheating at ide or while taxiing was normally not a problem.  Take off and climb cooling was marginal at OAT over 70 deg while cooling at cruise was good.  I have since changed to a belly scoop system with much improved take off and climb cooling.  

I don't know of a convention for expressing inlet area with respect to the lip shape.  An inlet duct divergent area change from 16.5 sq in to 27 sq in in a short distance indicated the potential for air flow separation from the duct wall and turbulence in the duct at the air flow velocities likely to be generated in flight.  From your additional description, this would not seem to be a concern.