I have an extra 750F windjammer bracket! Just kidding, no I really do, but kidding you might need one. I used to make mufflers for the 75/76 F exhaust. Slash cut 2 1/2" x 3 1/2" X 18" not beautiful but sound awesome. Used a glasspack from a cobra sidepipe. I may see if I can source parts to make a muffler for the 77/78 header, the collector is way smaller.
Let us know what you need.