There could be damages from different times or the side impact could have done it, i have to say that to me the damage does not look like it was wholly caused by a side impact, but that doesn't matter, these cars have seen action for 40+ years, as Adam said take good measurements, if it is within your means, level the car on jacks in a way that the front frame rails are not supported by any of the jacks that you are using (but still safe and secure), then place a level across the front end of the rails to see if one rail is higher than the other one. It it is level, you are good to go, if the passenger side is slightly higher then you have to deal with it whether you are replacing the inner fender or you decide to straighten it out, you need to make sure the rail(s) not bent. People say +/- 1/8" is close, but its up to you to make that call.
One last thing, it looks like you have removed the k frame, which makes life easier but while you are at it, make sure the k_frame is not twisted. If you need to know how, let me know!