The hole in the side of the cowl is to allow clearance for the throttle linkage. Even with it's design, the fit of the engine is tight in width, and the carb is mounted on the side with the glow plug on top and exhaust at the bottom. The full scale spit has a smaller bulge at that point and I may cover it with an oversized version. It should add a little more flow but not much. There is also a small cutout in the plastic that the stacks are mounted to allow for clearance for the carb itself.
Yes, I have seen the 5 blade spit. It's nice to see others attempting to go for a more scale prop. I know the APC blade that I am using doesn't come close to the scale outline of the real prop, but to me, it still looks a lot better than a 12 to 14" 2 blade. If he gets that 5 blade working well, it'll be a big head turner at the airfield.

Scott