Good point. I see a different casting number for regular C body manifolds but not for Magnum manifolds. Do those get different castings as well?
On another (related) topic, I talked to a guy about doing a run of these. Best case, you could break even with 25 sets, but it could also be 60 sets. That would mean you're out somewhere between $30k and $72k, and you wouldn't even make a nickel in that case.
No wonder the manifolds are marked "not eligible for discount" on the website!