Done and done!
Returning the smushed filter would have been more hassle than worth it so I figured if it wouldn't jam in there I'd just buy another. Left it in the sun on the dash all day to soften it up and it went in fine. Nice and snug, foam gaskets look like it has it sealed and no need for tape to hold it in or seal it off.
It is an awkward place to try to get at to do the cut out though. Still so worth it and I'm going to love the filtered air.
One more item crossed off the list
Much thanks again to the wonderful support here!