Unless I am reading your post wrong, you will have an FG20 "for a heli or something" left over. Why not put that FG20 in your GP 76" cub on floats, instead of either the .65 or the FG14? Then, when you want to, you can use that FG20 for something else.

Unless, you just want an FG14, then youi do not need to justify buying it, just do it!..

Sincerely,

Richard