Carriage bolt holes for wood bed

[HKanada182]

Afternoon lads,

I have searched this forum high and low, and all of the other internets for some information. I could not come up with anything to solve my problem, and I really do not think I am the first to come across this.

I found some decent bed sides that needed a little repair (see pictures) They were off a 67 and I got a 72 so I added side marker light holes, and needed to repair the inside lip where the bed side bolts to the wood floor and through the cross members. My issues is this: How does anyone get a square hole into the steel? I am hoping the wood is strong enough to hold the square on the bolt in place, but I would feel a lot better if I had the steel bedside flange to hold the carriage mounting bolt. Aside from drilling a hole just a bit smaller than the square and filing the corners in, I am out of ideas for how to get this to work. Has anyone out there 1/ replaced these flanges and 2/ what did you do to hold to carriage bolt??

Thanks all,

Mark