Chuck,
From what I've read in old articles, the Spacebug has a little more performance than a Black Widow. There was a racing carb and head that you could buy that would add about a 5-10% speed increase, depending on prop used. I assume the head was just a high compression head like you would use on a later TeeDee. Not sure how a different carb would work, other than just screwing a larger inlet to the venturi tube.
These stepped cylinders are the early style. I'm not sure exactly when Cox went away from them, but I like them. Interestingly, since this is an early engine, the glow head of the later engines will not work on a Spacebug. The bottom of the glow head is narrower than the later glow plugs. Hopefully this glow head is good, as I only have one spare head with the narrower bottom.
This is an abomination in my mind. Drilling holes in a Babe Bee tank is alright. It only takes a couple of minutes to replace the drilled out tank with a new/used one, and old Babe Bee tanks are everywhere since people often swapped them out for the 8cc tanks.
Mark