Those floats are around 42" long and will work just fine, although they are heavy. My brother has a senior on 34" floats and they work just as well. The general rule of thumb is to use floats that are 75%-80% of the fuselage length, which makes the 42" floats the right size. The reason the 34" floats work is that the Kadet is so light it doesn't need the floation provided by the larger floats.
As Jim suggested, place the float step under the CG or a little behind it. Keep the top of the floats parallel with the bottom of the wing, and adjust the height so that there is around 2-3 inches between the top of the floats and the bottom of the prop arc. The spacing between the two floats should be around 25% of the wing span. Hope this helps.....Seaplane