Rear upper control arm spacing issue

[Perkster029]

So I'm happily plodding along, managed to get both front control arm assemblies mounted, and I move on to the rear.

I get it lifted into place, insert the bolt, put on the nut, and I notice these awful gaps. These are not torqued down, yet, but the front was nothing like this. We're specifically looking at the rear passenger upper control arm.
(edit: these are donor control arms from a 2000 C5. Bushings have not been replaced)

Overview:
IMG_20180817_191430552.jpg

Rearward mount:
IMG_20180817_191444386.jpg

Forward mount:
IMG_20180817_191452801.jpg

This can't be right, can it? I don't want to just put a washer in there, that doesn't seem right either....

Thoughts? Anyone experienced something similar?