Earth-31 is loosely based on Chuck Dixon's story LEATHERWING. Published in 1994, it was one of the original annuals to carry the ELSEWORLDS branding.
Earth-32 is very loosely based on Mike W. Barr's BATMAN: IN DARKEST KNIGHT from 1994. Other stories that featured a similar "fusion" concept included J.M. DeMatteis' SUPERMAN: SPEEDING BULLETS in 1993 and Michael Green and Mike Johnson's MASH UP in 2009.