Yes thicker.. look them up on Summit, they should have a thickness.. .60
If it's cast iron to cast iron you can probably get away with just regular felpro gaskets. It should be a flat machine surface. I use a permatex product called The Right stuff.. and black.. they have gray but I use black. It's not cheap.. honestly I use it on absolutely everything and have had great results..
My process for an intake manifold gasket is to make sure both surfaces obviously are clean as you can possibly get them and I even take a little rubbing alcohol, odorless mineral spirits, or even a shot of carb cleaner or brake cleaner on a paper towel and wipe everything the manifold the heads the China walls until they're whisper clean.. I then hang my intake gaskets on coat hanger wires and use a product from Edelbrock called gaskacinch.. don't quote me on the spelling on that.. it's like a rubber cement and a little jar that has the little cotton ball on a stick attached to the lid. First I wiped that where the gaskets are going to go down on the heads.. then I wipe it on both sides of both gaskets is there hanging in the air... Don't be in a rush cuz that stuff wants you to let it sit for 10 or 15 minutes anyways... When I do my double bead of the right stuff on the front and rear China Wall I put a little extra in the corners great where the head meets the block on all four corners. I then take a small smear and smear it around all four of the water ports I even take a small smear and put it on the intake manifold around all four water ports even though the backs are closed. Again that is a very thin smear not any kind of thick coating... I also put a single pass on the intake manifold in the China wall which is the front and the back so the two meet each other...
I lower it down on obviously being very careful to try and hit it directly the first try I put a bolt in the easiest one I can find in the far back and then go kitty corner to the far front. Get all my bolts in loose and then tighten from the center circling my way out to the outside. After I have it tight and then I've ran the car up to temperature and let it cool off I try and tighten it one more time cold...
