For the custom cube dispensers, you should have the textures on the mappacks's "custom" folder, named "cubedispenser#.png", where the # is the id you set up to the entity in the editor
Disclaimer: it's possible that the rightclick menu for cube droppers is broken in the editor
Portalsides seems to control which sides of a tile are portalable. Notentitiessides seems to control whether funnels and lasers can go through the block (and if you have custom collision sides, only those sides filter), and entitysides seem to only affect cubes. My code was a mess and the documentation is non-existent, and I used to do a lot of very small changes/additions only for my own use in very specific cases, so I had a bit of a hard time finding out what everything did.
Sorry there isn't much I can do at the moment, but this mod is several years old and it's never been properly optimized and bugfixed :/