"How can you be so sure that Kimber wasn't screwed together, crooked?"
Why would that make a difference. The mounts go on one piece - the receiver.
I had this same difficulty with two Winchester 70 Classics. Ran completely out of scope adjustment. Instead of shimming I chose to take metal off one of the scope mounts and it worked very well on both rifles. I used stones and polishing paper and tried and fit and tried and fit until I got it where I needed it.
