Maybe this will help.
The hole is 7 1/2" x 5" and the strip at the back is 2 1/2" wide.
I can get the cowl off by moving it forward till it clears the prop hub then rotate it down
and lower it from around the muffler.
I don't know if its the 3 to 1 ratio or not, but no engine problems and I didn't cut the tubes.