Phantom
Concerning the instructions calling for zero incidence all I can say is yea sure, this is the number one reason so many have so much trouble. The fact is you need a minimum of two degrees positive and more normally four.

In reguards to the Cubs ventral fin Yes it will fly without it Perhaps with a bit of a butt wiggle during a steep turn as you pull elevator.

On a Full scale cub the requirement for the ventral is entirely dependant upon the STC used for that particular manufacturers and model float also you will find differances in the various STC's on float instalations for J-3, PA-11 and PA-18 Supercubs as well as the many differant long and short wing pipers.

John