I don't know what an Ag-King 30-40 is, but when I needed a new muffler-and-pipe for our old Kubota L245DT, I took the measurements to the local NAPA auto parts store and they produced a reasonable facsimile for me. It was a muffler with the proper pipes to clamp on each end, as opposed to the original equipment being a one-piece welded unit, so it looks a little different, but it works fine. It sticks straight up in the air and the original had a curved end, but for the new one I got one of those little flapper caps for the end.