Get some perf board or etch your own board with resist paint if you want a decent other side ground plane, some Schrack relays, a couple of trigger transistors, a few resistors and womp up your own. His schematic shows in the photo. While your at it add a gas discharge across the input along with a bi- directional diode chip to ground, and with a couple of capacitors. MDR will be affected a bit but not noticeable in ordinary usage. These circuits are pretty well documented these days.