Thanks for the comments!
If the tractor sat unused for 30 years, I can't imagine why it would have some much built up carbon. I would say that is not normal.
The muffler can be bought new from Carter and Gruenwald: http://www.cngco.com/Index.cfm
Type in "185" in the search field for some of their available part, others youll have to call and ask for. The muffler is a bit expensive at $109.50 though.
I'll have more updates on my progress soon!