The McCoy 40 Blue Head was the same as the other 35 & 40 McCoys with a simple air bleed carburetor and an exhaust baffle that would close with the throttle body of the carb via a link. Because of the introduction of the Hi-Low K&B fuel of the time, the end of the piston connecting rod was bushed on a few models, but not all of them.
The bushing helped to reduce the wear on the wrist pin during low throttle operation. This bushed Conrad would also fit in a Red Head. For the most part, they were pretty good engines.
Mikey