For a head that has had the guides machined for additional clearance, I like to use a viton seal. They seem very forgiving, easy to install and dont split like the teflon ones.

Too many cars, too many parts, too little coin, too little space to work in, too little time left to make it all happen! Update: down to one ride, still too many parts, a little more jingle in the pocket, gaining space, and it's going to happen this year!