Sorry for the late reply, only just reread this thread my bad
hissing contant whilst your foots on the brake pedal indicates split diaphragm in the servo if its inside the car, otherwise it could be a faulty vac line to the servo,
your master cylinder, i wouldnt think you'd have an issue with, everyone went on about how you can roll the seals on them, I went to the trouble of getting an old one from a scrappies and stripping it down, its near on impossible to roll them, you'll have to be very unlucky if you do,
the master cylinder has 2 chambers, with 2 bleed nipples, one controlling the front offside and rear nearside, and the other controlling the front near side and rear offside, ( same with any car)
you're best bleeding the master cylinder by pumping the pedal BUT only half way, do not put your foot to the floor***, do both nipples at the same time, with some aquatic air line on each one, each about a metre long, air bubbles in the master cylinder will cause soggy pedal

(do this with the engine running to you'l clear it far quicker, just make sure the res is full)
hope this helps