So just for the record, the master cylinder has 3 main seals.
All of them are sized for the cylinder bore which is 13/16" (or .813"). Two of them are .400" ID. The shaft which the middle seal slides over is .554".
Raybestos kit MK1026 has the two outer seals and they appear to be identical.
I have ordered one more kit that looks like it may have the middle seal.
Hopefully this works!!