A.I.R. (Air Injection Reaction) cross over tube. That's gonna be a TOUGH part to find. I would replace it ONLY if the truck has to pass emissions. Otherwise, I would block it off. Of course, I GUESS if you are going for a 100% restoration........
doesn't need to pass inspection.. not sure what to do.. damn thing is so original its a shame to not keep it that way but hell if i keep the stuff i take off i guess it really doesn't matter..:) maybe slap a set of headers on the *****..