The headset has the mic in the setup with the ear pieces, which runs to the connection that replaces the hand-held mic which is removed. No need for it with this setup.
Very cool! Curious about why you tied in an external antenna.
If someone else is interested in this type of set up, you may want to check out airrider.com. They have a cb that mounts very similarly and will tie in with a headset. Friends of mine have dealt with them and we're very satisfied. Also, GWRRA members qualify for a discount.