"I have been thinking about this for awhile now. I thought the answer was pretty obvious. If you are using S10 front brakes, and S10 rear brakes, - why not just use the appropriate S10 master cylinder? But, I think there are both manual and power brake S10s out there ( at least in the 1980's). Do they use the same or different master cylinders? Can you get a power brake master cylinder and not use the power booster? "
I've got the single piston S10 brakes (80's vintage) and thought the same as you, so I ordered an S10 non-power brake MC (the parts catalogues list two separate numbers for power and non-power brakes) and installed it. I admittedly have never driven a car w/o power brakes before, but the pedal seems very stiff. It stops the car and everything appears to be functioning, but it takes a LOT of leg power to do so. Also, it seems as though there is not very much stroke to the pedal. This is a head scratcher as I assumed that the matched S10 components would work well together, the only thing I can think of is that I was actually given a power brake MC, which means the bore is larger than it should be. After having the winter months to think about it and seeing this thread I have an itch to try the same master as Fred (73astregt).
I read through the posts and would like to be certain of the MC that you have used successfully: Is it a late 70's Camaro MC for non-power brake applications? If not please correct me. Also, a part # and brand would be awesome when you have the time to post.