That would depend on the wing loading. As long as the wing loading is under 30 ounces per sq. ft. you should be ok. (25 would be nicer.) At 10 1/2 pounds (after you paint the floats) you wing area needs to be at least 806 sq. in. If it isn't, find a lighter airplane for those floats and a lighter set of floats for that airplane.

I don't think you will enjoy the way an ST 75 flies 10.5 pounds either.

Jim