I hear you,  My 71 super is the worst car ever to bled brakes, Like Travis said,  make sure the all the pads are adjusted till they scrape the drums. This seems like the main thing that worked. Each wheel has 2 star spurs that are rusted and worn and when you've been upside down under the car for 30 minutes, trying to set them,  you forget which way they go  to tighten and end up loosening them.  I hate them dohickeys

Things I have tried. 
Loosen  the lines at the master and squish out all the air from the master cyl,

  I even jacked up the rear of the car hoping the air bubbles would drift to the rear cyl's

Press the pedal real slow,  fast stomping makes 1 big air bubble in to a million small ones

I had a rusted bad  line that runs next to the drivers accelerater pedal under the carpet.

Those black flexi hoses to the wheels look good on the out side  and can be mush rubber inside,  so if the bleed fluid is black,  change em

I think I returned perfect good master cly's when I did not have the pads set on wheels tight.

I'm sure I'll remember more or the horrors of the car, tomorrow
SC