cutting intake valve guide for postive seal?

anyone running a positive seal on their intake valve guide? any input on pros and cons..
Thanks
Paul

 

Buick used a little seal that looked like a o ring .... I have used a ford umbrella type.... or a perfect circle type.... all will work..... but the nailheads get no exhaust side seal...... that why it is entirely ''normal'' to get a puff of white smoke when you start a nail up.....

 

Went with the felpro type and the shop were I took them for valve job cut the guides for clearance.