If it were mine, since it is bent I would wonder what's up with that, whether it is too small, or too weak, and considering the slight cost of a bolt I'd replace it.
I could not find a part #, so what I would do is look at the bolt on the other side spindle, same position. A ruler could be hit or miss but calipers, you can get an idea of the length, and as far as diameter it's going to be metric, medium-coarse thread (see what's available, you need a matching nut), and hardened to class 8.8 or better 10.9.
If the bolt on the other side was also replaced with the incorrect part, I'd still measure it and wonder if what happened was that someone used a the next size down in a standard rather than metric bolt size, see if it looks like the slightly larger metric bolt would fit. Again calipers are going to be much easier to use than a ruler, but if worst came to worst you could just pick up 2-3 different metric sizes at the hardware store then use the one that fits tightest.
Any bolt you choose should have a shank that extends past the BJ stud contact area, or better if closer to completely through both sides of the spindle, so threads are starting near the point where the nut is tightened down then if you need a washer to make that work, add one... I can't recall, maybe it has a washer or flange nut? If it has a flange nut (on the other side which is possibly the original or correct part?) then do add a washer if the replacement nut isn't a flange nut.
On a fastener this old, I would prefer a new bolt to one from a junkyard but this may depend on location, vehicle fasteners here tend to rust enough that sometimes you're lucky to get them off non-destructively, especially around the suspension where wheels kick up water and salted snow slush.