I've searched the forum for third brake light options, and there are some very clever ones out there. My 76 has the PORSCHE reflector on the rear panel, and I figured, why not use that for a third brake light? Working with Tony Miller of Translog in York, PA, we came up with this solution using two strips of LED white lights:
Here's how it looks on the car:
To fabricate the light, Tony had to grind off the silver reflector material where the lights were glued to the lens:
and of course tap into the brake light wiring, but it was a fairly simple process. The result is acceptable to me, perhaps not as noticeable as a higher-mounted solution, but it will hopefully improve the car's visibility when braking.