I work in the “Industry”
I love Ghostbusters so I just used my connections to get what I wanted
I have a full size ECTO-1 too

My Pack is actually from the ones made for the Universal Florida Show. it was one I traded work for. I modifyed it to be even more accurate to the original film.
The prop people that made them started with a pull for the original Ghostbusters mold and cleaned it up, The mold was pretty bad by then, and did a new mold.
I have access to a mold that was made off of one of thoes Packs (the mold for the Universal packs mold is also gone) and I know where all the parts that were attached to the pack came from, a lot are still there if you know where to look.

and the alice frames are not too hard to find. My brother in law and I have been trying to get the project off the ground for a year now. havent heard too much interest, if there are a few people that want them we will go ahead and do them
Joseph
Joseph