With facing 603 cylinder heads the issue is not neccessarily the prechamber issue; there is a clear and exact remedy for dealing with the effects of reducing overall cylinder head height and the resultant excessive protrusion of the prechamber tip into the combustion chamber. The problem very quickly becomes the valve's position which can not be modified within the dimensions of the head.

The minimum height after machining is 142.4 mm (the cylinder head starts with 142.9-143.1 mm) and the maximum removal is only 0.5 mm the maximum deviation longitudinal (lengthwise) is maximum of 0.08 mm.

You would need to know the numbers that define the dimensions of warpage before spending money on a cylinder head damaged beyond correction.