A modular upper-door assembly including a standard geometric corner component and a standard geometric B-pillar component for all vehicle model doors. Each header, belt and window-track has a different length and bend geometry for each vehicle model door while each respective component shares a standard geometric cross-section. All headers may connect to the corner component and B-pillar component in the same locations for each vehicle model door. All belts may connect to the corner component in the same location for each vehicle model door, but the attachment location on the B-pillar may vary from vehicle to vehicle. A stationary-glass or mirror-sail may also be overmolded into the assembly.