packp3d is just a program to pack a game into a p3d file. It is itself a .p3d file (packp3d.p3d but I think there also is a exe version in the windows sdk).
The ‘runtime’ is just a luncher type program that knows how to run .p3d files. It’s not connected to any sdk version, but it downloads the needed files (packages) from runtime.panda3d.org, so the needed files need to be there.
Not sure if that made anything more clear.
As to what I did - installed the runtime (same old 1.0.4 we have for years), downloaded packp3d1.9.p3d and run it via the consolle with some options. That’s all.