Re: is this the correct float for a HS6 carb on a
I don't know if this helps or not. To quote Moss Motors, "SU replacement floats with moulded bosses for the pin are the only ones available. To use these & obtain the correct 1/16" to 3/16" gap between the float & lid, a shim may be required under the needle & seat assembly."
It appears that you have the opposite problem of not enough gap. If the float chamber lid gaskets were missing it would effectively lower the float level as you say.
I don't really know what the problem may be but multiple lid gaskets would raise the floats & allow more flow. If the shims between needle seat & carb body are present, maybe they can be removed.
The 1/16 to 3/16 between float & lid should be measured with the spring in the needle not compressed.
Sorry I'm not more help. Maybe someone else will know? See if the attached scan helps.
D