"designed for the Pontiac racing cylinder head that bolts onto a Chevrolet Big Block engine. It "cannot" be used on any Big Block Chevrolet design cylinder head."
These valve covers have been around for years from GM Performance Parts and are being discontinued by Gm, 5 sets are available from vintage. Pontiac had a set of heads that bolted on to the chevy big blocks, of course these are discontinued also, and these covers were available to bolt onto those heads. They used to sell for $350.00 pr, not sure what the price is now. If memory serves me right they would bolt on to any Pontiac engine cylinder head.