I use to run a similar arrangement in the 'hippo-tipo' 825. Except, no hatch. Fuse top header, and the pipe mount took a bit of work from inside the fuselage. Pipe tunnel had side vents, and exhaust exited the bottom of the fuselage
I really have to find a rainy day with nobody to bother me....... then I can scan in a bunch of older photos and stuff. Would be nice archive of history
