The float should be parallell to the base of the carb (where the bowl meets the carb. You just bend the tang on the float with the carb inverted. The weight of the float is sufficient for checking.
It's been years since I've replaced a float needle and seat. I remember it was either on a B&S or Tec, that little rubber seat has ridges on one side. "Those" ridges go down (in first) I used to use an allen wrench to push them in. A no no I used to do when removing those seats was to put my air blow gun into the fuel inlet and blow the seat out at my fellow mechanic. That was in my youth.