I don't know if the contact fingers and drum segments are universal across all Lionel E units, or whether Lionel used different units depending upon application (1-motor locomotive vs 2-motor). It would seem from a quick thought process that if an E unit in a 2-motor unit is robust enough for 2 motors, then installing that same E unit in a single-motor unit, and MU'ing the contacts to a second, single motor unit, it would work OK.
You could, of course, convert the E unit to an electronic one, perhaps from Dallee or a similar company. The manufacturer would be able to tell you the current-handling capacity of their product, and you could measure the start current of your two motors to ensure success.
