RE: ****please HELP****Floats on a Nexstar
As usual, Mr. Seaplane nails it. Take a look at where your landing gear attaches to the plane and be sure the hard points ar in the floats and sufficiently reinforced to accept the loads.
Another landing gear block just in front of the windscreen bulkhead is a good place to attach struts, as is a block just aft of the bulkhead at the rear of the cabin. Get a 1/4" thick plywood strip about 3/4" wide and epoxy it inside the bottom of the fuselage, especially being careful to bond it to the sides and to the adjcaent bulkhead. The standard factory-installed block will be just behind the CG, as that is the appropriate place for tri-gear mains. One option, it's not pretty but you CAN make a T-shaped strut and install it in the existing nose-gear block. Just remember to disable the nose-gear steering. The advantage of this is that it does provide for easy experimentation with the incidence of the floats: Loosening the nose gear attach collars and sliding the strut up and down makes incidence adjustment very easy.
The GP floats are larger and heavier than other floats. They perform beautifully on the water, but you may find your plane laboring to haul them around the sky. You can get some really efficient (light and durable) foam-core floats that will give better performance then the GP floats. Mr. Seaplane even makes floats that have become the standard by which others are compared.
In an unrelated note: I find that this post is number 1000 for me in this forum. Everybody run aou into the front yard and yell WooHoo!