My vote says one-off (An internet search was fruitless), possibly adapted from something designed for the F-series (They seem to like the aesthetics of having a bolt every two inches screwed into their truck...
)
Here's a clickable link to the same ad:
https://losangeles.craigslist.org/ws...854960053.html
All else fails, bounce the guy an email/text? In the past when I have reached out to others selling 4x4 vans, most have been straight up about what's what, where it came from, etc. I realize that a lot of sellers probably don't want to get spammed with those kinds of requests, but I haven't had anyone tell me to go take a long walk off a short pier, yet.