polishing the back of the nlet valves is a very good idea. It drastically reduces the amount of carbon that can build up here and restrict flow. I did this with 2 power drills, a vice, some emery tape, and some imagination...
shows the valve pocket area after we opened it up. Its the area above the valve guide in this pic. You can also see the tapered guide and 3 angle seat, which is blended into the chamber as much as possible.
showing tapered valve guide, and reduced guide boss (the alloy bump in front of the guide). Often the boss is totally removed. this is my old SSS L head, but shows some of the principles of mild DIY porting.