I think you need to pull the pans to get at the bolts. I parted out a sled recently and I pulled after the pans were off I don't think there was enough room to pull the bolts out with the pans in because the bolts run the entire width of the arm
I'v had to change both a-arms on my brothers Z370 which is the same chassis...and you do need to take just that side belly pan off to get to the other bolts for the a-arms. And taking the belly pan off didnt really take to much time. So the whole thing shouldnt take a whole lot of time.