I ran a Thrush welded muffler on the KJ for several years until it rusted out. Now onto a rockauto stainless thru-flow type.
No jobber tailpipe I jave found is as good as the original so far as good diameter and not rusting away quickly. I used up the first one, and now onto another used one. The section of pipe from the cat flange to the muffler is easy to renew so long as you can weld.