The plans of the Aurora ask the same procedure, grind a groove to the wing bottom skin for pipe clearance. After all components put into position, I decided not to open the bottom skin. There is enough room for the pipe. If the pipe is centered between wing bottom skin and belly pan maybe 1/4" space on both sides is there. I marginally ground a flat spot, and glassing the wing center section was a standard procedure anyway. I am using the red pipe for the OS .61RF Hanno Special, but I think it is same diameter as the other Hatori pipes for .61 engines.

Interesting to see that the belly pan is not enclosing the cylinder head on the Beetle design. It fully conceales the engine on the Aurora. Does anybody know if engine overheating was an issue with the Aurora?