Valve stem protrusion length

Hi Guys,

My cylinder head machinist asked me to see if I can provide him with what he calls “the valve stem protrusion length”. I have looked high and low in all of the data that I have and I can’t find this distance.

Does anyone know if Norton ever published a specification for the length that the valve stem protrudes past the bottom of the valve spring pocket for the RH4 head?

Thank you,
G Jensen

Installed valve spring height would be the spec I would use. So would any competent automotive machinist.