How fast is the stock HOR with a .28 or .32?
I think the wing will be okay, but the tail might need some reinforcement.... IMHO, the plane would be more "appropriately" powered with a .25-.28.
Unless your landing area is a pile of large jagged rocks, the muffler won't get scratched up. We land them in the grass all the time.
Put landing gear on it like a BUHOR, and you'll have something pretty neat. The muffler won't get scratched up, either.