Basicly when you play with the Classic AT Rules you play a game that is almost exactly the same as the original AT. Basicly the Classic.at2 file is the same as the generic.ptmaster file (from AT). There are however a few minor differences.

For playing with the Classic AT rules I advise to use the Classic AT Manual PDF that should be shipped with AT Gold.

*Rulevar(833) disables the use of battlestack in classic.at2, if you load generic.ptmaster directly the scenario will not block the new battlestack rules.

*You can now use supply for engineers operations from higher HQs, overseas is also ok.

*Upgrades no longer need their supply from a land connected HQ, overseas is also ok.

*You can now transfer units and they'll keep a part of their AP if they are transferred using “own power”