Kultulz to the rescue
Those plates look kind of neat, I wonder if they work.
I was thinking about some of the Parker intake port stuffers for the Cleveland I'm building right now, but they are a pain because you need to fill the floor of the intake runners with epoxy to match. ( it probably wouldn't be a bad idea to do the same for those plates though)
I never knew they made anything out of sheet metal for the exhaust side.
( I remember the ones that were about 1' thick and the head was machined with a ledge for them to sit on)
I wonder if there is any real gain from the exhaust restrictor plates?