OK, so basically once I have a plane flying correctly and then add floats, I need to make sure that the plane balances at the original CG WITH the floats installed, making sure the float step is lined up with the CG.
You put it all together in one nice sentence. That's it, exactly.
I thought I read in the GP 40 size float kit instructions that when installing floats, the CG should be moved back 1/2 inch from normal land flying. Does this sound right?
Moving the CG back will make the plane more responsive/tail heavy. I don't know why they would want you to move the CG back. I've never heard of float instructions saying that. Are you sure they didn't say something like "put the step of the float 1/2 inch behind the CG"? That would make more sense, but I could be wrong.