That is a little confusing to me. If the size of the holes in the cowling is equal to the size of the cylinder and head then the entire front would be open. From the pictures I am looking at, that is not the case.

I attached my picture again with yellow outline to distinguish between the fuse, cowl and spinner. There is a little flat area (less the 3/8")in front of the carb that could not be avoided on this engine. The front of the carb comes up to the nose ring and spinner and I saw no other options. My Jett engines will work out a little better in this area.

I have tested different props over and over before and this may end up being similar to get the best results. I read that a cowled engine can give you up to 12% increase in speed. If I get 1/2 that and not burn up my engine I will be happy for awhile.

Thanks for your input