It’s the same as any other 5/16 bolt, which is 25 foot pound, or close to it.
Not sure how many options there are for W2 exhaust gaskets. If you are using adapter plates I use orange silicone between the head and the plate and no gasket. Then I use a gasket between the header and the plate.
If you don’t need the adapter plates then probably you’ll use what you can get.
