There is a support ring/plate under the tunnel that either the auto shifter body (one version) or manual shifter boot screws into. The console is mounted via a bracket and riv-nuts. The shifters just pass through the console and some trim pieces.
The AIM has some pictures of the reinforcement in the auto trans section. I just fabbed up about 1/2 of mine that was hacked out at one point when someone installed an inline shifter... I'm pretty sure someone posted measurements of the tunnel cut out/opening over on Team Camaro. As far as the reinforcement itself, I don't remember seeing anything there, though I was just browsing. If you buy the boot trim ring/retainer or auto shifter, the reinforcement closely follows that shape (I don't know that for a fact on the auto). It's just a bit wider than the boot trim and has a slight U shape treatment to the edges. You can see that detail in the AIM.