First off, here's the dyno graph of the corrected (SAE) HP and Torque curves:
The first dyno run produced 429 RWHP with a virtually straight HP curve. By the end of the run, the coolant temp had risen from 190F to about 220F. I let it cool down to 200F, and then did a second run. This run was identical to the first up to the point where the car made 400 HP, at which point the HP curve abruptly flattened as though it had been planed off. Coolant temp rose to about 225F. At that point, we rolled out a fan and pointed it at the front of the car (from underneath, the dyno is raised) to help keep the car cool. With the temps back down to 190F, we did a third run, the one recorded above. Interestingly, the third run shows substantially more midrange torque than the first run, no doubt a function of the cooler air reaching the air intake. Lesson: make sure you use a fan during dyno runs to (a) keep the engine cool, and (b) keep the intake air at close to ambient.
Next up: K&N air filters and Hennessey smooth tubes, and another dyno run...