modify 65 column dual cable shift for later single shift 904

Not sure. The previous owner had it on jack stands for 5-6 years. He never drove it and claimed that it would not shift out of park. He pulled the linkage/pan and said something fell out. He did not know where the broken part was so I was not sure where to start fixing it. I've since pulled the trans and its sitting on my garage floor.
If it would not shift out of park, it could easily be a problem in the cable linkage and not in the trans. at all. But now there's parts missing, so it's time to get on top of this and figure out what the problem actually is. Post photos like CudaFactHackJob said and try to get an idea what fell out. Check the shift cables, make sure they're intact and move freely when you move the shift lever. Find out what you've got to deal with and then make decisions and move on from there.