I've got two Chemtex machines in my shop that came with a van I bought last year. A 20-45 and a 27-47, both with HX like yours. One end of the marine exhaust to to the engine exhaust and the other curls back to return through the frame tube to exit out the front, one on each side.
I've not tried to start them, I'm a diehard 4cyl guy.
You live in beautiful country, I've been there several times.