I second what Texmo said. I brought my intake and exhaust manifolds (separated) into work and used our cabinet blaster. You wouldn't believe what came out of the exhaust manifold! It was a huge, nasty, rusty cloud inside the blast cabinet for at least a minute. It really felt good knowing that I was taking 50 years of garbage out of the manifold. Make sure they blow a lot of air through all of the ports to get any residue and blast material out. Then I painted the manifold with Cast Blast paint. I think it's rated to 1,500 degrees. It looks like brand new. Good luck.
