Metric Rear upper trailing arm question.

  So, I am new to this and have questions i am unable to get answers for around my local track. the car I plan on running is used but in good condition. The previous owner had good luck with it. While i was taking it apart to check everything i noticed that the passenger side bolt was gone in the upper trailing arm where it mounts to the rear end housing. The car is a 78 Monte. I didn't think much about it at first. Then started doing a little investigation. Looking at other cars i noticed that several owners are doing the same on one side or the other. I've asked a few of them about it and they all seem to be tight lipped concerning the matter. I understand because I've been around racing my whole life and know how racers are LOL. I am hoping that some of you kind folks here could explain this to me. Any help would be greatly appreciated thank you all.