These heads were Low Mile castings but they got wet at one time and most of the valves rusted badly . That is why I went with the New Valves . The Factory Springs Looked to be re-useable but at $30.00 dollars for the Z/28 Springs it was a great up grade . Good stock springs set up right are said to work with up to 450" Lift without problems . Max Lift Clearance I would say 500" but any thing over 480" I would check them . But no these early heads do not have the clearance problems Like the stock Vortec Heads do . If your heads are in really good shape I would run them with one of the many 454" Lift Camshaft Brands out there .