(due to overscan, I presume).
It's not overscan, but nominal analogue blanking. When calculating PARs and DARs, only the central 704 pixels (702 for PAL) should be taken into account.
It's simpler to ignore width completely when trying to work these things out. To go from PAL non-anamorphic to NTSC anamorphic just multiply the height by the NTSC/PAL ratio (480/576) and then by the anamorphic ratio (4/3).
326*(480/576)*(4/3)=~362.
DE