Removed exhaust manifold and found something interesting

I had about the same thing with a 340 HP manifold, but in the process of removing the stuff, one of those steel sleeves came out. I took that to a machine shop, and the guy made me 2 solid plugs. I knocked the other sleeve out, and replaced them with the plugs he made me. They have been on the engine in my Challenger since 1990, and never a problem. Plus side is, the manifold could be easily put back to original with a now available heat riser kit. Not gonna happen in my lifetime! LOL