How about a source? I don't generally consider it wise to take technical advice from someone with something to sell. Especially when they hint that normal operation might require more and more expensive race engine parts rather that a simple pin, as suggested in the first link below.
Link makes it look like a Manley valve brochure.
I maintain my position:
http://www.cdxetextbook.com/engines/comp/vlves/valverotation.html
https://books.google.com/books?id=D...onepage&q=valve rotation in an engine&f=false