2225541 is correct for 67 a bodies with manual brakes with front disk. That isn’t the part number but the casting number on the underside of the master cylinder.
There is also a casting date on them.NOS. I got one that doesn't have a date code stamped in the side, so I think that means it's earlier than '69.
NOS Brake Master Cylinder 70 Plymouth Duster w/ Front Disc Brakes 1970 | eBay
There is also a casting date on them.
Dan,
I have a nice one 150.00 plus shipping