Here's another long shot. Some of the old metal base cabinets had a french cleat mounting system that incorporated an upside down "J" on the back of the cabinet and a corresponding right side up "J" mounted to the wall. They were designed to keep the cabinet to the wall and liftable to get out.
Once you get the countertop off, look down the back of the cabinet against the wall to see if that's what's there. Unscrew/unbolt each cabinet from each other, and try lifting straight up to remove. If not, move to plan "B".
PLAN "B": Get the countertop off and really check all around the back edge to see if there are any screws. There maybe one or two you can't find easily. If this doesn't work, move to Plan "C".
PLAN "C": Grab a 10lb sledge hammer and knock the heck out of it into smithereens.