Master Cylinder Differences?

Ran into this last year for 75 Duster. I tried Advance and Pep Boys - both looked like what you found. I got this one at Autozone for under $20. It is the 15/16 bore (P# 1571 I think), which (contrary to the what the auto store specs show ) is original to the car from what I can tell. It has disk front and 10" drum rear, slant 6. You said 1-1/8, I did not see that size - everything I looked at was either 15/16 or 1-1/32. The other place I saw the round front style was if you can find an NOS Wagner - there were a couple on ebay when I was looking, but a bit more expensive and I did not want to wait for shipping.
Just an FYI on finish -so you don't make the same mistake I did. I thought these had a coating on from manf. Mine was covered with rust in a couple months. If I had known that I would have cleaned it and clear coated before installing. So ended up painting it black....