I bet that car rides like your living room couch
The olds 350 and the chevy 350 have about....hmmm 6 bolts in common. They are very different. Olds engines look a whole lota like. You need to check the block casting # to be sure. The Olds big block is simply a raised deck version of the small block.
To id the engine for sure look here. If its a 350 the number will be 395558. The pictures below show a 403 and a 425.
If its a 455 the number will be 396021.
I would like to suggest you buy these valve cover gaskets, they are awsome.
I say have fun and enjoy.