Hey I just dug one of these out of my engine pile :-) Eager beaver I-SX
If you do a search for " Featherlite " here in the conversion forum you'll find many 18cc and 21cc ideas.

I'm building a 106" span floater Pawnee clone, 1920sq-in and just a big putt-putt AP ship. They have a long nose so the little 21 on EI will do the trick.
Good luck with yours!