I just finished a ucd with a kb61 with a pitts muffler on it. I didn't have to shim anything but I mounted the engine horizontally and had to go absolutely crazy on the cowl with my dremel.

Hovers great with the .61.

definately try to get some kind of fuel regulatory. Tank position does suck. I'm using one of those old school control line deals. (syringe and tubing).

have fun. super cool plane