I spent Friday night and Saturday rebuilding the entire brake system. Fresh rebuilt calipers on the front and rear. I also installed the Russell braided hoses I've had sitting around for the past year. The rear calipers were completely siezed. I broke the C-clamp trying to compress one of them. The hose to the rear end was collapsed internally, as was the passenger side front hose.
Everything's good now. I bench bled the master cylinder and pressure bled the system. It's got all new fluid throughout.
Got in the car and pedal to the floor again.
Came inside and started researching some more. Found out that the booster needs 15" of vacuum to operate properly and that some people have to buy vacuum reserve canisters to compensate for bigger cams. Went outside to find out mine's pulling only 11" of vacuum.
I put the MityVac on it and pumped it up to 15" and started the car. The pedal was nice and firm. SO I drove all the way to Summit and bought a reserve canister. The brakes are now better, but the pedal still goes down quite considerably and isn't anywhere near as firm as it was with the MityVac on it.
The canister holds above 15". Of course, when you hit the brakes, it takes vacuum out and falls below 15". I discovered that my booster needs a minimum of 15" for a firm pedal.
Has anyone else run into this and how did you fix it? A vacuum pump is out of the question as of right now and I really don't want to be driving around with squirrely brakes.

 

rear calipers should not be compressed by a c clamp........there is a special tool to use on it and it turns clock wise and counter clock wise. i do not know to much about the boosters but i just had to have one put in my blazer, my pedal always felt soft and moved a decent amount and didnt think much of it since i baught it cheap, old and abused. but replaced the booster and it firmed up the pedal alot. not sure if it would help in your situation, but mine was like 60 or 90 bucks i think and i think its the same as in our camaros.

 

Try bleeding again - I know, you've bled til your blue. I bled mine every afternoon for a week before I got mine.

Also, if you still think it's a vacuum issue, a trick I used was to bump up the timing a tad, and lower the idle. I got up to 11" of vacuum doing this - mine was below 9 before with my cam and tune - but the increased timing and lowering the carb idle kept me in tune, and increased the vacuum on mine to around 11", which gave me plenty of brake. My timing is at about 12* BTDC on a 350, mild cam, Edelbrock Performer RPM intake, and Edelbrock 600cfm 4 bbl. - try timing up a degree at a time, lowering idle to compensate, and test it - it's worth a shot.