hey Pease, can't wait to see the pics!
The Briggs muffler many of us 4-stroke guys use is the 4-8 or the 5-7 horse muffler.
Home Depot and Ace have it for under $10. Looks like this: Arnold M-110 Muffler 4-8Hp Bs294599
Sorry I can't help with the flexpipe, I sourced mine from another member who had a roll of it.