I was able to use new carriage bolts on my 1 ton truck running boards
I had to cut them down to perfect length first
I think I bolted the brackets to the running board, left it loose and then bolted it all up to the frame. Trying to line up all the carriage bolts to frame mounted brackets might have been too challenging.
But it was a long time ago and I’m hazy on how exactly I managed to do it without help.