I bought a used K6 Wee. The previous owner did a muffler mod by cutting off the piggie and drilled 7-3/8th holes in the outer chamber. It worked pretty well and wasn't too loud, but it had an annoying sound when decelerating. Chuff Chuff Chuff.
I decided to make my own mod to see if I could cure this sound. I didn't want to recover the 7 holes drilled in the outer chamber because I felt it gave lower back pressure and thus better fuel economy.
My fix was to chop the top 1/2 inch section off of a propane canister (Yes, I was careful in that chore.....) and weld it over the series of holes drilled in the chamber. I drilled a slightly larger central hole in the propane top than the old stock unit (1 1/4 vs 1"stock) and used a short section of exhaust pipe taken from an older riding mower.
Now it looks like stock and is a bit quieter than before, I think it was a good compromise.