After looking closer they look similar to what I bought years ago for my first van - a 5.6 Ford cargo - mine were made of stainless steel and mounted into my rain gutter - and I attached perforated angle iron from passenger to driver side with them and then built a "Walmart style black plastic outdoor plant rack" (open air style) and set down into the angle iron for roof rack.
The brackets were used to mount a roof rack on top of Hollywood vehicles to shoot down onto moving movie scenes - I used mine to photo grizzly bears in Denali NP - to meet park regs for safety reasons - I took my roof ladder off - just in case the bears knew how to climb up ?!