Model originally uploaded to Thingiverse at https://www.thingiverse.com/thing:2591310.
After accidentally breaking my 20 year old Millennium Falcon model in a blind VR frenzy, repairing it, I took the opportunity to replace the half-ass engine replacement I originally put in.
The original 1970s AMT/ERTL Millennium Falcon model had a lit engine, so it came with a clear plastic cover for the area. Later manufacturing of the model got rid of the engine light, keeping the clear plastic. So you wouldn't see into the inside of the Falcon (what a piece of junk!), you were suppose cut out a crappy grid from the instructions to you would paste over the clear plastic. I didn't like that, so instead I fashioned some hose clamps into a reasonable facsimile of what the engines might look like. At this point, we'd only seen the engine section when lit, and could see what looked like slats of some sort.
This new 3D print goes with the slats idea, but with sort of vanes, like you'd have on your car vents. Think thrust vectoring. This was based on John Martin's scratch built designs on starshipmodeler.com
New movies have shown it should be a double slat, but I prefer the look of this single row. Also, I was worried about visible ghosting with the supports.
Partly to reconcile the double decker look, and to provide some "internals" I created some greebles to go inside. Sort of a double decker set of exhaust nozzles. Without these, you can clearly see the inside of the plastic model, through the slats. There are cut-outs for the landing gear boxes.
John Martin's Millennium Falcon build: http://www.starshipmodeler.com/starwars/jm_mf.htm
Note: This is the model kit I used over 20 years ago: https://www.amazon.com/Star-Wars-Return-Millenium-Falcon/dp/B001AVM1L4/ref=pd_sbs_21_5?_encoding=UTF8&psc=1&refRID=KTKY8MPXN4T83JG9TCXJ