1...a few millimeters shouldn't harm anything...make sure the valve slides easily in the guide..
2..lap the valves..it should leave a dull area on the valve faces and seats..
You don't want to grind the valve stem. ...that's only done on non adjustable valvetrains..L head engines.
3...Make sure the block and head are clean and dry...Never grease a gasket..they'll never seal..
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