Just buy the HSN you need and run FAI fuel. Muffler from Bisson or Slimline is needed either way. Gas version is Very different, head (bigger) rod bearing etc. We run 20x10 or 21x10 Bolly props and they really haul. OS F plug, very wet prime, flip backwards. Running in can take a gallon or two if its not already done. Try to rotate 15degrees away from fully inverted to avoid drowning the plug.
jp