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:

• You could leave the covers off, with the holes plugged, nothing can get into the engine.
• Remove the vacuum controlled valve, plug the vacuum line coming from the carbs.
  • To remove the tube to the airbox:
    • Get two 1 1/4 diameter 1/4 inch fender washers and a 1/4-20 socket head bolt and LOCKNUT.
    • Put the bolt and one fender washer inside the airbox, put the other fender washer and the locknut on the bolt and tighten securely.
    • I am paranoid about having a bolt on the "clean" side of the air filter, so I used a locknut AND red Locktite.
      • NOTE: This is a real pain in the ass to accomplish if your hands are large.

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

• Plug the holes with bolts (JB Weld on the threads). Let sit overnight.
• Using a belt sander, remove as much of the raised area as possible. If you have access to a vertical mill, it would be even better.
• Plug airbox as described above.
• This does make removal of the valve cover marginally easier than simply plugging the holes and leaving the covers off.