Bill the casting number on my original '69 disc brake master cylinder is 2226821 and is listed for '67 -'69 B-body with disc brakes. It looks pretty much like the one in your photo and the 2223821 master cylinders are difficult to find even used. If he's not concerned about "numbers" find a suitable replacement (reman) and sell that one for decent $$$ if it is a 2226821. Personally, I would see about having it professionally rebuilt, again if it is a 2226821 master cylinder.