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The thermactor air injection should only go into the exhaust at the back of the heads and at the cats(except on some HD trucks that had it plumbed into the top of the exhaust manifolds as well.) Are you still running cats? No reason not to, and if you want to keep this system you'll need to replace the tube connecting the heads at the back. So assuming you have the system that injects air at the back of the heads, the headers need only an EGR port on cyl #1 and an O2 in the collector.
The thermactor air injection should only go into the exhaust at the back of the heads and at the cats(except on some HD trucks that had it plumbed into the top of the exhaust manifolds as well.) Are you still running cats? No reason not to, and if you want to keep this system you'll need to replace the tube connecting the heads at the back. So assuming you have the system that injects air at the back of the heads, the headers need only an EGR port on cyl #1 and an O2 in the collector.
Still have cats, the exhaust is unmolested so far.
The 351 also draws the EGR gases off the right side manifold. You'll need to do something there too. The Hedman shorty headers for these has the EGR connection.