You have done your homework N7OR....That set up on that plane should fly beautifully...That is if a pilot error doesn't occur....
OK now about the nose block..rsdonomoore is right, just get a couple of balsa blocks, epoxy them to the nose of the floats, sand to shape, and voila... The flat nose probably won't effect the take off, but if have nose down landing it could grab...(that's a big maybe)....