1994 S10 or Blazer, both will be bigger than stock with the blazer being the Biggest. I think the Blazer MC would be too big for stock brakes, I recommend using the Fiero MC, but you could probably get away with the S10 MC.
It is a little bigger than stock (I believe) and bolts right up and threads right up, but it will change your braking a little. You will be able to produce a little less line pressure at the same pedal effort, but pedal travel will be reduced.
I said 1994 because I have a 1994 Blazer MC in my Grand Am brake swap so I am certain that year will work.
Which master do you have. The one with the line out the end or out the middle? If the line is out the middle you can ask if they have or can get you a rebuild kit. If there is a clutch and brake rebuilder in your area they might carry them. Get a rebuild master kit for an 89 Jeep Cherokee. If the one with the line out he front end no ideas. I've never looked at my 88 to see which it has for sure.