Well doesn't the MF14 have a Kohler K321 in it? If it does just go to the exhaust shop and have them bend a piece of 1 1/2" pipe in a 90* bend with a 1' leg at the bottom and the other leg being however tall you may want it. Then just trim it to fit. The pipe fits right over the 1" NPT pipe that comes out of the head.
I got the two stacks I have for $25 including clamps. I checked into pricing for stainless stacks which I think would be great and I am sure if I have more quantity and interest I could get them cheaper but for one 1 1/2" mandrel bent stack in stainless is $68.