There are two AIR pumps on the 454. Each feeds fresh air into control valves above each exhaust manifold. These then pass air through a stainless steel manifold into threaded ports on located at each exhust port on the exhaust manifolds and up into the exhaust port up inside the head.
The concept of the AIR system is pretty simple and one of the early attempts at emissions control. Unburned fuel exiting from the head hits fresh oxygen pumped in from the AIR system, it's re-ignited in the exhaust port, manifold reducing the emissions. Of course, it also means placing a lot of restriction in the exhaust port (picture a small cigar sized tube right up next to your exhaust valve stem in the port) along with increased tubulence in the port and manifold from re-combustion in the exhuast exiting the engine. Lastly, think about the heat this generates in the manifold and we all wonder why RV exhaust manifolds are prone to heat stress and cracks.
I had cracks in the stainless manifols of the AIR system causing exhaust leaks. The price to replace the AIR manifold exceeded replacing the entire ecxhaust system with headers and free flow mufflers.
So I replaced them with headers and could no longer could use (or wanted to use) the system. So I removed the control boxes (located alongside each valve cover) all of the tubing and the upper AIR pump (the one that feeds the driver's side manifold.)
It was a simple removal of the top pump and a new belt to make it all work. I left the other pump in there to keep the alternator belt as is and it' just two darn cramped in there to get at the thing. So it now pumps air to the passenger fender well.
For the WP replacement, you would need to remove this pump for access from the top, or go with Brett's approach from the bottom.
If you leave the existing exhaust system you would need to replace the pump once you were done with the job.
1986 Airstream 345 Classic Motorhome