OK, here's a bit of an update...
I took my most powerful 25mm deep 80mm fan and made a few cuts so it could fit in the hole... (I think I got this fan out of a retired Dell rack server, if I recall)
Fitment success!
Just a bit of aluminum duct tape (my favorite!) to hold and seal it up...
I put everything back together and no fitment issues. I charged up a 7.2ah UPS battery and threw it on there. Man, it's a loud little fan (at 0.70amp draw, I expected as much), but putting my hand in front of the vent grill, you can feel the air being pulled through very well. I closed everything up and will see how the car feels in a few hours (if the battery lasts long enough, lol).
I'll eventually move to a dual smaller fan setup, but this was a quick way to test it out.
In other news: nearly done with the framing of my subwoofer box. Bought the fiberglass resin (bleh) and what nots to get the bottom/rear molded up. Also, got my Custom 3D printed shift knob! Gotta consider what I want to do to it before installation... might sand and paint, might leave as is! Hmmmmm...