Re: 3rd: 3D Viewer, needs j3d-1_5_2-windows-amd64 . zip
As you have seen, the auto-installation of Java3D no longer works since the website it is trying to download from is dead. If you found the file elsewere, try to put it in the jre/lib/ext folder in the ImageJ folder.
If this does not work, try this (at least it worked for me with ImageJ1.x):
Upgrade Java3D to 1.60 and use JOGL for the platform-files. You must download these files yourself. The advantage with this approach is that this works fine with Java 8, and is also compatible with all old ImageJ plugins so you can use BoneJ and any other legacy plugins you have which depends on the 3D_Viewer under Java 8, if you are using ImageJ 1.x (which you apparently do).
I also see today that there is now a Java 3D release version 1.7.0; but I haven't tried that. I tried the pre-release of 1.7.0 and that did NOT work when I were fiddling with this a couple of years ago.
If 3D_Viewer installs and launches without error, but just shows a grey window, you can add -Dsun.java2d.d3d=true as an option in your ImageJ.cfg file. At least this worked for me.