Dock Floats do not have a rating for river use, but I can tell you they are suitable for floating dock structures. There is no flow rate per minute value.
The dimensions are for the overall measurements.
My answer is no based on having a houseboat. You need much taller floats that can go under and not just on at the side. My houseboat is 16ft wide and my floats are 36x48x24 down on each side with a slight hangover for a 40ft boat. this is very stable and sites high enough that the wood does not touch the water. These floats are more for a smaller side deck. Over build floats for weight on the houseboat. You will have more weight than you expect with furniture, friends, family, and fun stuff.
6 plus 3 flat center support floats with the same 16" height. Use three on each side and the flats down the center.