[DonC]

In my humble opinion a dyno should be used only for break in and tuning for an engine and/or engine/drive train setup. Comparing dyno numbers from one engine to another is a waste of time if the numbers are from different dynos. As a RELATIVE indicator of engine health and setup, fine, but it shouldn't go any farther than that. The key word here is relative.
Just simple variables in setup of both the engine and the dyno when the numbers are generated can make significant differences in the results. Were the numbers taken when running with the engine's own water pump, alternator and other belt driven accessories or not? Exhaust through headers? Air filter on? etc., etc.
I'm more apt to believe someone who says they have about X hp than the person who gives a specific value.
Changing components for better performance, driveability, fuel efficiency, etc. when compared to a baseline before the changes, sure, but again, it's all relative and I have some relatives that I wouldn't touch with a ten foot pole.
DonC