1972 C60 Master Cylinder size help

[eodcoduto]

I can find most answers to my questions with the search function and Googling stuff, but I am stuck on this. I have a '72 C60 that is about back on the road, rebuilt the 366 and now I am working on the brakes. The master cylinder is shot, a rehone didn't help and I can't find a rebuild kit anywhere, so I am ready to get a new one. Now the issue is the master cylinder that I took off is a 1.5" bore, which should be right for a F070 7,500lb front axle, but I also have the 9000# spring option with a 23,000lb rear axle. So should this have the 1.75" bore master? Here is my RPO sheet, and any help is appreciated.

This is a 55K mile truck without rust and it is getting put back to work hauling bales and wood chips.