A lot of good information on that thread.
Just to add from what I've seen,the original ZL-2 Air cleaners have a small notch cut out on the right hand snorkle seam.It comes into play in the center of the seam.
It's about a 5/8 inch long,& 1/16th deep.The repro is one continuos seam.
Also I don't know if your Camaro thread meant this,but I have not seen a difference between a 1970 Chevelle Manual trans ZL-2 air cleaner,& an Auto trans.
Good thread!