Hi Phil,
If you haven't already found it I wrote up my Wyvern build in:
https://www.modelenginemaker.com/index.php/topic,8733.45.html .
I didn't use the original exhaust valve details with the valve seat made directly in the head casting, and I think that those were intended for a cast iron cylinder head. I couldn't see a valve seat cut in the Al casting that I had lasting very long, particularly for the exhaust. I didn't have to build up anything on the cylinder head with JBW other than some missing bits on the fins.
I made an error when drilling the ports from the valve seats to the outside world and drilled too close to the actual seat. That left the metal too thin and allowed it to distort when tightening into the head; see post #94 in the build log.
I've attached the drawing with the details of the valve gear as I made it as a .pdf. The cylinder head .pdf is too big for the Forum so that is attached as a .jpg.
If you think my drawings would be useful please PM me and I can send them.
David