Here is a 186s head I recently did up for a mate. Turned it into a 9 Port, fitted hardened stainless seats and Stainless valves with double valve springs were also fitted. I have a Mira Head milling machine able to cut out the old seats, will also cut out old valve guides for fitment of new bronze guides, - this head didn't get new guides though as these were still very good. I machine up new seats in the lathe and send them out for induction hardening. The head is cleaned and bead blasted in the cabinet, and surface ground before assembly of the valves.