A lead connector assembly for an Implantable Medical Device (IMD) is disclosed. The lead connector assembly includes a rigid elongated connector core having a core opening along its long axis. An alternating series of elastomer seals and header contacts are inserted into the core opening along the long axis and meet with an end stop to hermetically self-align the header contacts with contact openings along the sides of the core. A connector block can be inserted into an opening in the connector core, and sealed with an adhesive. Once the connector core, header contacts, seals, and connector block are subassembled, the connector core subassembly may be hermitically tested, and thereafter affixed to other subassemblies by affixing means on the connector cores. Feedthrough pins can then be connected to the header contacts through the contact openings, and overmolded with a header to the IPG's case.