So I am in the process of rebuilding a Spiderbox and have gone through the engine and even added an aftermarket cam and all kinds of new parts for it. The only issue I have run into is figuring out which exhaust gasket I am supposed to use with this new aftermarket exhaust kit I bought. I purchased a new exhaust stud kit and it comes with two different types of exhaust gaskets. One is a round thick gasket and the other one is a the shape of the exhaust flange area. Am I supposed to use both or just one of them? Attached is a pic of the kit I bought.

My Spiderbox only had the thick round gasket because the header pipe went slightly into exhaust port. You will use that one unless you have some kind of custom header that is flush on the end.

Yes, the aftermarket one is completely flush on the end. The center pipe does not protrude into the port like the stock pipe did.

Take a look how much the round gasket provides from the port surface when seated. You may end up using both.