I have a 1993 s10 chassis and pedal assemble in my 1952 GMC. I have installed 11" camaro front disc with 11" Grande Marquis rear disc. I do not know what master cyclinder to use? I would assume a S10 or Bravada with front and rear disc?
Get one that runs with 2 disks. Make sure your year of s10 came with 4 disc brakes and not 2 discs and 2 drums...Search RockAuto, I did that right now for you but I cannot post the link for some reason. Did your year s10 come with 4 discs? If it did, just get the normal master for the s10
Obviously you will need a master cylinder for 4-wheel disc.
Measure the area of your caliper pistons, and get a master cylinder with a bore size about 15-18 % of that area.
There's lots of info out there, you will just have to dig.
If you used one with a 1"bore, you will be very close, but NOT smaller !!
BTW, make sure you use a proportioning valve for an all-disc setup.