Kevin,

   The builder in Calif claiming 370 hp is Performance Aero Engines.  They do that on all of their large bore normally aspirated Lyc/Cont engines with the 10:1 pistons.  To my knowledge, they do not dyno the motors and have no way to verify the hp that they stamp on the engine's data plate.  I'd be very wary of the hp claim unless you personally see it on a dyno or get a printout from a dyno run.  I don't believe they can provide one.

   If you want to be sure, Barrett Performance Engines in Tulsa does dyno their engines and will give you a printout of the data from it.  Whatever they tell you, you can take to the bank.

   Skip Slater