regarding custom built valve guides I have some in my CVH the chap that did them made them from trojen.

He really knows his stuff my exhaust valves water cooled too! A finned extension in the water jacket! this really dumps heat out of the head well! you only have to ask about the lotus head work he has done!

He does a lot of marine work too! but is normally willing to do bespoke automotive work!
I think its because it keeps him warm in the winter!

http://www.bottomline.im/

hope this helps