Valve cover.
Reed valve pocket.
Inside view showing the passage to exhaust port.

Tap holes 5/16-18.
No drilling is necessary

Be sure to use cutting fluid.

Now it is up to you.
If you would like to keep the stock look, buy eight 5/16-18 setscrews, screw one in each hole about 3/4 inch then screw another setscrew in until it contacts the first setscrew.  Tighten it securely to lock them both in place.  Put the original covers on and you are done.

Alternate method 1:

Alternate method 2: (For those who just can't leave well enough alone)