Here is my Camaro with the GM done, now i cut off the mounts years ago and moved them instedad of just redrilling.
you do not have to move the bolt holes BACK as the GM shows, if your using a tubular UCA that has caster built into it. The rear bolt hole for the upper control arm gets very close to the Chicane bracket. here is a pictuer of it all installed on my car with the bracket cut off and moved.
Here is the original ATS Chicane as you can see the Chicane bracket is in a slightly different location on both. See how the rear of the Chicane bracket mounts to the original UCA mount and on the one above it is mounted forward of the UCA mount.
In the top picture I ended up with 8 deg of caster and -.25 camber. but it is a drag car
hope that helps.