M1A2SEP has a different engine. As far as the M1A1 vs. "M1A1HA", the "M1A1HA" is just a model company term. The "M1A1HA" is usually referred to as a Heavy Common and has an additional layer of depleted uranium mesh sandwiched between the armor frontal turret and hull armor. Uranium is a heavy metal, hence the term heavy. Common comes from the fact that the original M1A1 had changes made to it so it could be used by the Marine Corps. Hence the term Common.
There were some minor fitting changes here and there between early M1A1S and late such as tracks, deletion of retaining ring, uparmored dog house, but most of these changes were retrofitted to early M1A1s, so none of these are good indentification features. The only good way to determine the difference is bu looking at the serial number. If there is a U after the number, it is a Heavy Common.