The serial (COM1) and parallel (LPT1) ports are implemented on the motherboard; there is a 10pin and 26pin header respectively near the Erase CMOS button and SATA connector.
To bring these connections to the outside of the case an optional cable is available from HP "Serial and parallel I/O adapter (USDT) - PD825A". It plugs into the headers and is installed in the expansion slot.
If obtaining a PD825A proves difficult, an industry standard parallel and/or serial motherboard to I/O slot adaptor cable can be used with modification. The BIOS senses the presence of the adaptor and if not present the parallel and serial ports do not appear in the BIOS nor are visible to the Operating System; don't appear in Device Manager.
The parallel adaptor cable has 25 wires, the motherboard end IDC connector has 26 pins; pin 26 is not connected. Add a wire to connect pin 26 to pin16. The BIOS will sense the presence of the adaptor cable, the parallel port will appear in BIOS under Security and will be seen by the Operating System.
Similar arrangement for the serial adaptor; pin 10 is not connected, connect to pin 9.
A neat way to add the connection is to disassemble the IDC connector and remove the ribbon cable.
Move the connector an inch up the cable, cut off the protruding cable except the for the wire on pin 16 (parallel) or on pin 9 (serial). Fold the single wire around and back into the connector for pin 26 (parallel) or pin 10 (serial). Assemble the connector and squeese together to press the cable onto the connections.
The commonly available parallel cables all seem to be standardised on one wiring.
The commonly available serial cables come with two wirings; the one needed has connections pin 1to pin 1, 2 to 2, 3 to 3 etc.
All done, enjoy the two extra ports.