Whats the original M54 Cylinder head Thickness?

[megadrive]

hey y'all

Im have blown exaust valve and am currently replacing it. However, I wanted to find out what is the orginal cylinder head thickness is before I decide whether to resurface it or not because I suspect it has been resurfaced before by the previous owners and if that is the case I would have to use a thicker gasket since it would be the second resurfacing if not the 3rd. The heads can only be resurfaced a number if times and thicker gasket need to be put in to compensate the lost surface if it is too much. So does anyone have the specs for the orginal head thickness as I cannot find it?

I measured my head flatness warpage, it is currently 0.15mm(0.006inch) Is that within the acceptable tollerance?

Thank You!