A stop bath is recommended for C41 and apparently also ECP-2D. The bleach recipes for ECP-2D include two versions of an Ammonium Ferric PDTA bleach which sounds like what Flexicolor Bleach III for C41 uses. One big difference I see is fixer pH for ECP-2D vs. C41, so in theory a C41 fixer would need some extra Acetic Acid to get its pH down from 6.5 to 5.8, otherwise you risk off colors.