66,

I just took a look at the pics I snapped and reviewed your question. It looks like they may be cold riveted or some sort of a blind screw (chicago screw type) assembly. It may be that there is enough room for a nut and bolt but I would ONLY use grade 8 hardware on it. That assembly is under a lot of tension and grade 5 might shear off...just a thought.. I would use lock-tight on the nut as well IMO.

Good luck

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Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.Albert Einstein