Stan, how much exposed valve guide do you need for the seals? Are you just going to install a longer valve guide or split the difference and cut the guide boss also?
I like to see .250" minimum of the guide sticking up above the boss in order to do seals. Most stock guides have somewhere .250-270". There is no spec for this, so it is sort of hit or miss. The guides that were in the heads had maybe half that. No way would there be enough there to grip the seal.