[wdfifteen]

Look up a man named Wendel Kelch in Bethel, Ohio. If he doesn’t have a spare pump he may know someone who has one. He may already have a pattern for a new casting. I think the AW and MW both used the same pump.
Wendel has gathered a stable of craftsmen who can make nearly anything from metal or wood. Wendel is at the epicenter of all things old IH. He has done some amazing work. He restored a 1917 JohnDeere experimental tractor starting with not much more than a cracked engine case and some photos.
Also, LeRoy Baumgardner in Pennsylvania has tons of original early IH engineering drawings, he is likely to have the drawings for that casting.
These guys routinely make missing parts for one of a kind old cars, trucks, and tractors.