As I said at the start, the required pedal pressure was way too high (the wheel cylinders, hoses, lines are all OK) and I suspect the dual master cylinder set up requires boost for the best result. Anyway, a proven, simple solution for me with my other cars has been to just add a remote booster to the stock set up. I understand the positive aspect of a dual master setup (safety) but I find it mildly irritating doing plug changes etc while working around a dual master and booster in the engine bay.
But to get started on the change back to original I had to know what original was with master cylinder and pushrod. Internet searches are great but sellers don't always describe accurately or use correct images and being over here in Oz you have to be very careful what you are buying from USA. Shipping is a killer and returns are often impractical. For example the bolt spacing thing was confusing me because vendors/sellers were listing cylinders for 57 and 58 as the same and throwing Edsels/Mercurys/trucks etc into the mix. On checking the bolt spacing on my 57 firewall and my 56 Customline, they are the same so I know what I need. And I bought a push rod off Ebay after triple checking it was what I needed. I quickly add there are a lot of hidden differences between US models and Aussie models starting around 56 and we just didn't get your 57 at all (we just tarted up our 56 with a few Meteor bits and an Fordomatic,etc ) I'm getting side tracked.
Back to the shed.