Well, lets start with the base gasket You're using now, if it is the thin std. type, you will be adding another of the same plus the thickness of the shield at a minimum. They are
a "trim to fit" deal, You may or may not have to. The fuel line routing is again key because as the fuel in the carb evaps, the needle & seat will allow more in if it is trying to get
in, heat=vapor=expansion=pressure=more going in to the carb to evap while it's just sitting there.