Do a current draw test to find out what is drawing current. Just because you removed the fuses that are hot all the time doesn't mean that there may not be a short or possibly a relay sticking causing an accessory to draw. You should have no more then 50ma of draw on the battery. That is the maximum you would want to see. Anything more then that, there is something wrong.
Also check to see if you have any fusible links. I don't know if they used them in the 80's, but who knows? You may also have a shorted battery cell. Try removing all your fuses, it could be a ground sided switch, shorted to ground before the switch.