Do not use an 11x10 prop on an La 40 that would be disasterous. An 11x7 may well be to much for this engine also.

My speculation my well be no more than a 11x4 and that may well not get the airplane off the ground within your runway.

I am itimately familiar with this airplane having assembled/modified many of them and trained new pylon racers with this great little airplane and I know you do not want to hear this but must say it. You are not ready for this airplane and the results are very predictable if you do not seek mentoring i.e. A little help from an experianced flyer of this type airplane.

John