RE: twist 3d for a fun fly/ what engine?
FWIW, you know a 61FX is .1 oz heavier than a 91FX (per O.S. website) dont ya? And a 91 would be GROSSLY over powered.
Dont know if there would be clearance to swing the wood a 91 would require.
Try a YS 63 or Saito 72/82.
Just my $.02