Those little rings are 38 to 40 rear rocker box spacers. They press into the rear exhaust hole in the rocker box. These little buggers are tough to get out of the rocker box. You usually have to heat them up and pull them out.
Here is the hole that the spacer presses into. The sealer is #2 permatex. It works good, we use it for sealing fittings too.
Here is a pic of the spacer being pressed into the head. After the piece is pressed in, you have to wipe off the excess #2 permatex.
The finished product! This is a really cool detail.