Yes
Leave the portion of the original pan in place that covers the cross member piece.
I put the hump on the automatic floor pan and traced the flange. Offset from the tracing using the width of the flange then made my cuts. I made some plug welds in the piece of the original pan to secure...
Here are some links to another site that my be helpful.
https://forum.e-bodies.org/cuda-and-challenger-general-discussion-roseville-moparts/2/blackout/20301/
https://forum.e-bodies.org/body-shop/5/rear-seat-black-out/29669/;topicseen
When you do this project, please start a thread on it and include detailed photos. Long ago I had book marked a thread that documented this but its gone. I recall reading that the foams were different but I could be wrong.
E-Bodies.org site is having a site recovery presently, so my links don't work.
There are a couple of good threads over there on restoration of plastic panels. Titles are:
"Repairing wasted door panels and textured plastic"
"Interior Plastic Restoration Journey"
Also this one...