I have a car repair in Brazil and a customer brought me an Oldsmobile Omega 74 to redo a cylinder head. I took the grinding and there was no solution, I looked for days on the internet for this cylinder head and I didn't find anything for the Rocket 350 5.7 I just read that there is a way to fit a big block cylinder head in a small block. If anyone has a link to a store that they can send to Brazil, it would be of great help, but if you can talk more about this fitting, I would also be grateful. Sorry if the translation is not good, I'm using google translator. Here below, pictures of the broken cylinder head

 

It appears that the cylinder head casting number is 411929. It should have a large number 8 cast beside the exhaust port of the number 1 cylinder. That cylinder head should be plentiful as it was available on the 350 Oldsmobile motor from 1973 to about 1980. You should place a post for a number 8 cylinder head in the "parts wanted" section of the "Oldsmobile parts" section in the "classifieds".

 

To answer your question about using big block heads, they will bolt in place and all external dimensions and accessory attachment points are the same as a small block head, but the intake ports are much larger and you may have trouble getting a good seal on the intake manifold as a result. The combustion chamber on the big block head is much larger than the combustion chamber of the number 8 cylinder head so that low compression motor would have even lower compression. Not a good option in most cases.