Jeep/AMC made a major change from '79 to '80. '79 was the last year that TH400 and Quadratrac was used, in '80 they went to TF727 trannies on the slush side. I would assume that following the same logic, they figured "let's change everything at once", which is why your two trannies differ. I'm fairly fluent on '79, but '80 is a whole new ball game.
Rich