Andy, I know it’s a bit tough but stick with it. Pull the seat and move the seat supports over 1/4 – 1/2″ with a big rubber hammer–or whatever big heavy tough thing you have laying around. That should allow the clutch to clear. You could also cut off the left side seat support and use a bolt on model, which would give you more options still.
We’ve mounted a Pro Gas Animal (same dimensions as a 206) on a TopKart Cadet, now that was tight. We had a 206 on a 2007 Intrepid, and we’re planning on putting one on a TopKart 102. So far I haven’t seen any show stopping problems.
It’s going to be tight, but look a little harder at possible solutions.