The only film I can remember that used E-3 was Ektachrome Professional from the 1960s. The process was related to E-4, but not the same. That means it required benzyl alcohol or a similar solvent in the color developer to release the couplers. It can not be processed in E-6 (or C-41) chemicals. As I recall, it could be processed in E-4 as a one-shot only, with somewhat inferior results, but I don't know what modifications to the process were needed. Incidentally, Ektachrome Professional was an outstanding film. I believe it was only available in 120.