318 Connecting Rods and Crankshaft

A Serdi is a valve and guide machine that uses cutters instead of stones
you have different cutters that can cut multiple angles and widths at the same time including a top and bottom cut which you can then easily hand blend in for quickie "bowl blend"- there are other vendors
(you can also use multiple cutters for uncommon jobs)
you can have the top cut round into a unshrouding of the valves
more area around the periphery of the valve can give more flow
Too much and the flow then hits the top of the cylinder and the sharp ridge causes turbulence and shear
that's why sometimes you need to relieve/ bevel/ break the edge of the top of the cylinder (but stay above the location of top ring travel)
That's why I suggested comparing the bore to the chamber with a dykem and scribe

are you following this thread
302 casting on a set of 318 heads
good luck with your build
everyone here is here to help