Head gasket question

Been wanting to get other stuff from RA anyhow which I just did to "water down" the shipping cost, so I'll have 2 full sets of the marine ones.
I looked up the standard fel pro head gaskets there and price wise these marine ones are only a couple of bucks more than the standard fel pros. Without closeout prices the marine's were about double compared to the standard ones.
They also show a "severe duty" for a 318. All listed for the 318 show same bore sizes as each other.
For the marine ones you have to put the PN in the "universal look up" section for them to come up

Of what I saw somewhere I found a description of their marine ones, the core on these are"300 series stainless" but didn't specify 304, 316, or exactly what. They are slightly thinner than the normal "perma torque" ones ...