Which master cylinder

[JA50N]

I am in the process of swapping 1 ton axles into my 1986 GMC K10. The dana 60 has the J8 calipers (I think), the rotors are 1.5" thick. I am in the process of swapping the 11" rear drums to 13" drums to make sure the E-brake will work with my current setup (14 bolt is out of a '78 so it has the old style E-brake).

My question is 2 fold, a) will I need a new master cylinder and b) if so which one? I am thinking one from a single rear tire K30 will do the trick but I am not sure. Any help will be appreciated.