You started the thread asking what type of airplane this is yet you are quick to say that it is not a modified Skybolt (R) model? I am a little confused...do you know what the airplane is or not? You do know that an (R) model is a radial powered Skybolt don't you? A very popular radial for the (R) model and the Pitts 12 is the M14P radial as seen on this bird.

I am not saying that this is indeed a Skybolt (R), but it does have come very similar characteristics although as I stated before there are a few things that are throwing me off. The one pictured below does not have the louvers on the engine, but it does have the open cockpit and you can see the similarities.