Aluminum heads and steel shim gaskets ?
Multi layer steel. I took the rivets out and coated every later with spray on copper coat. Held up fine on every engine so far. Had one MLS problem motor. X block with Batten heads no copper coat and dripped water when cold. As soon as I got heat in it the drip sealed.
We just did a 340 with Edelbrocks. used Felpro 1008's worked fine but only 10.5 compresion.
Some motors with boost and MLS My son cuts a ring under the fire ring and adds a inkinal wire . He just did a Cummins with that wire. Very common on pulling tractors