Implantable medical devices include header structures with conductive paths from the feedthrough conductors that may be located on one side of the device to electrical connectors that may be located on an opposite side of the device. The conductive paths may include conductive interconnect pins and lead frame conductors. The conductive interconnect pins may be located in holes present in a header body where the conductive interconnect pins are attached to the feedthrough conductors on one end and are attached to the lead frame conductors on the opposite end. The lead frame conductors then extend to the corresponding electrical connectors. The header body may provide cavities on each side to allow for the insertion of stack assemblies that include the electrical connectors and lead frame conductors.