RE: J3 cub, crash on take off nearly every time.
Toe-In is the wrong way to go.
If you look at the dynamics, toe-in will make the plane more unstable.
If the plane swerves to the LEFT on the runway, the weight is transferred to the RIGHT main.
If the right main has toe-in, this makes the swerve to the left more pronounced.
Instead add just a small amount of toe-out to each main wheel.
Now the weight transfer from a swerve will act to pull the plane back into a straight line.
I didn't believe it at first either when I was first told about this.
I have since tried it on all my .60 sized WW2 fighters IT WORKS!