I have a nice 4-1 with Muffler that I took off of my 71-750K1. looks good on the bike. I have the mounting hardware, new exhaust gaskets and bracket that mounts the muffler to the upper shock stud. A litle surface rust mostly hidden when mounted,but VERY solid and sounded nice on the bike.. Biggest thing to me was, it ran well with stock jets.
I was going to post it for sale but if you are interested I will take some pix.
I was told it was an early Jardine 4-1 and has no writing on it but part #11414 on the muffler flange.
Bob