The Plymouth 440 Six Barrel / 440+6 ("Six Pack" is the Dodge brand terminology) is referred to as a "Wedge" motor, because the combustion chambers are wedge-shaped. The Hemi has hemispherical combustion chambers. Performance-wise, the 440+6 will hang with the Hemi until you get into the upper RPM ranges.
Beautiful car, BTW, but all Mopars are beautiful - even the ugly ones.