I used the Inline Tube kit with parking brakes and it works better than good - IT's GREAT! My opinion of course lol. We have the blazer front spindles converted to LS6 rotors and pads - holy schmoly - night and day compared to the stock stuff. I would recommend the Inline Tube stuff to anyone - their support is GREAT. These brakes with the biggest front and rear sway bars available makes it feel like a modern car in terms of turning and handling.
It's about $800 worth of brakes, but if you can get your G-body cranked up to 150mph, then you'll feel better with it - trust me. I had the stock parts in the 140 range and I felt as if my life was in my 40 year old brakes (can you say poop stained underwear lol!)
Don't cheap out on brakes - life and death.
Regarding the master cylinder and proportioning valve, it depends on the year of the booster you have. There is a large bore and small bore diameter master cylinder. I have a thread about this a year or two ago. If you have an older brake booster, either '80 or '81 before then you need the small diameter M/C. I used a small bore M/C for an '80 Riviera - worked PERFECT. Search for the thread and you'll see what I mean.