There is a spec for that I'm sure. I remove the valve springs and make sure the valve travels smooth but not much side to side play.
If your cylinder and rings are that nice, it's most likely the valve seals. But, your correct, you can replace the valve seals but a sloppy valve guide will wear out the new seal in time.
Out of all the 350X heads I've dealt with, I haven't found bad valve guides yet.
I have that pin in my shop, I can get you the OD and OAL if you shovel the snow out from it
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country