What you need to grind away is part of the cylinder head where the air injection port is. I've been there, had to do it. Drop the exhaust pipe, take the manifold off and take the gasket off, then lay the manifold back up against the head. Just behind the steering column, you'll see the portion of the manifold that drops down and curves in towards the block hit the head.

Then there is the joy of reaching it with a grinder.

Good luck!

Jim Burch