The 68030 was a 68020 leaving out a couple of rarely used instructions (I don't recall what) and adding a sort-of-but-not-exact subset of the 68851 MMU, 256 byte cache and some bus interface improvements (sync access). That and process improvements made it more efficient than the 68020. Motorola also upped the clock speeds on the 68030 (up to 50MHz).

The EC chips, at least at the beginning, had a defective MMU that was disabled and sold cheaper than a 'full' chip. Fine for the Amiga OS, or embedded stuff. I don't know if they ever made them without the MMU at all. The EC nomenclature extended to the 68040 and 68060, where it meant "no MMU or FPU", and added the LC nomenclature which means "MMU, but no FPU".