I think ADA rings work in the domes. Cant help you on the gasket.... no o-rings there either?
i have an older twist head, and it's got just the orings I believe, if I used a gasket it was a stock one but I am pretty sure I didn't use a gasket because the water porting on the head is completely different than stock. Mine isn't the sawblade design, it was one before that I believe