I have an 82CE and have never felt like the brake pedal travel was correct as it seemed to almost go to the floor but still stopped the car.  Never tried to slam them on though.  I had looked over all the lines and calipers and found no leaks so figured I had a bad MC and the fluid was looking dark since it hadn't been changed in a while.  Bench bleed a new MC, installed it, bleed the brakes according to the shop manual and the pedal was not any better, maybe even worse. 

Decided I would bleed them again, and then another time and still no better.  As soon as I start the car up the pedal goes to the floor with light pressure, but still stops.  Decided to do an isolation test on the system to see if I could find an issue with one caliper possibly.  Clamped off all four lines and have a firm pedal. Checking pedal travel with only one line unclamped each time and did not significantly change the pedal travel.  Disconnected all clamps, pedal drops significantly.  After talking with a couple people, I decided to reverse bleed this time thinking air wants to rise so what the heck, might as well try it.  Fired up the car, pedal to the floor.  All total I have went through 4 large bottles of brake fluid bleeding them.

Decided I might have one of two issues since I am not finding any air in the system, bad new MC or something wrong with the booster?  Think MC is good since I have good pedal in the isolation test with all lines clamped.  Checked vacuum and have around 17" going to the booster.  Checked the vacuum check valve and it seems to be working correctly.  Left the vacuum disconnected and the pedal travel seemed about right when I ran the car and applied them.  Hooked up the vacuum to the booster and the pedal goes straight to the floor.

Do I have a bad booster causing this?  Heard they are a 'pita' to change so want to make sure.  Thanks for any advice.

Two issues I’ve found in the past.  Old brake hoses & old bleeder screws letting air past the  threads. 

My money is on a bad booster.

Started looking at cost for a new booster and noticed that the ones on the 82 year were yellow zinc plated as noted to be correct versions.  Went and looked at some pictures of some others and they all had zinc plated boosters on them.  Now thinking at some point someone changed this one out since mine is not and might not be the correct one to truly fit the car.  Still not sure why this would make the pedal drop all the way to the floor even if not 100% correct.

A bad/leaking booster wouldn't cause the pedal to go to the floor.  It would cause a hard pedal.

Another suggestion would be to bleed the MC with the front of the MC higher than the back of it.  

What method are you using to bleed the brakes?

I bench bleed the master before installing it.  Have bleed 3 times using a single person method and pumped out all the air.  Then this last time did a reverse bleed and pushed it backwards to the master.  Bleed all four wheels each time and did the inner caliper on the rear first.  Had the front of the car higher than the back and followed the shop manual instructions.

Do not understand why the pedal is high with no booster vacuum hooked up and then goes straight to the floor once hooked up.  I can isolate each caliper by clamping the hoses and have good pedal with only one line unclammped.  As soon as all are open, straight to the floor.  Even having just the back two or just the front two clamped, good pedal travel.

I never knew how the vacuum booster on power brakes worked. But it seems to be the common element in your problem here. I'll check around and see what I can find out. 

You have air in the system. I would highly recommend using a pressure bleeder. You can manually bleed these things until you are blue in the face, and still have air. Get/borrow a pressure bleeder, and make it a one man job. Using a rubber mallet on the calipers as you bleed will also help dislodge any air bubbles that are invariably stuck in the calipers. 

I fully agree with the above. Make sure you keep the fluid level from going low or you will be doing it all for nothing