This is a good question. a few years back I was doing the 11.75 disk brake swap and ordered an 80's vintage van/truck master cylinder and it came back in iron. It's so much lighter than the stock one i didn't even notice till I got home. I will use it anyhow, but i was bummed that it wasn't aluminum. I recently went to Napa armed with numbers for an aluminum unit and they have zero in stock and order from the aftermarket. I think Master Power Brakes sells em.