RE: Foam Seawind EP from Great Planes...
My first suggestion would be to direct your question to Great Planes while you wait for someone with appropriate knowledge to respond on the forum. You are using a heavier motor and a heavy battery. The motor might not fit in the preinstalled motor mount, as well. Other than these remarks, I can't help.
Have not flown mine yet. On G4 flight sim, it tends to fly nose down and skip on the water when landing. I have cartwheeled it several times due to wing dipping. I intend to fly off snow or grass, first.