Wow - I nabbed a set of those very aluminum housings off ebay a year or more ago with the intentions of making them into side mounted back-up lights & have been looking the last few nights at high power white LEDs to equip them with...
It's great I finally know where & what they originally belonged to...
Someone online commented the LEDs sounded like an expensive solution when fog lamps or some such would work, I really want the back end of the 27-footer to look like something out of Close Encounters of the Third Kind
if and when I am attempting an emergency half mile back up to make a U-Turn some when in the future..
If I were to try and replace the reflector insert I'd be looking at truck stops or truckers after-market replacement shops online. Let us know what you find!
Here is the photo by goldenlily
from their User Gallery..