Anybody know what these are for?
Here you go! From a past Accessory Of The Day post in 2010.
these can also be used to mount a set of running board gas,oil,and water cans. I think it would be fairly easy to build your own holder for a set of these cans and mount it to those brackets for a no holes in running board mount.You see lots of the cans at swap meets and on Tbay but not so many holders.