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.