In this pic you can see the board clamped to the table of the mill and getting machined for the plug. I believe that I counter bored the hole to a depth of .300. The plugs that I made have a .005 press fit, which is ideal for aluminum. I am still going to weld them in, just for the sake of safety.
Here is a pic of the board mounted on the bike, the bloody finger is in the pic for scale.