Extracting .unity3d files from Unity 3.4.2 for upgrade to Unity 5.2.3

I'm attempting to upgrade a project from an old Unity version to a less-old Unity version:

Original Unity version: 3.4.2 (released October 2011)
Target Unity version: 5.2.3 (released November 2015)

(FYI, the reason why I am not upgrading to a more recent version of Unity is due to a dependency on a third-party library, Active Reader, and 5.2.3 is the highest version it is compatible with.)

The issue that I'm facing is that in the older Unity, project assets were dealt with in a completely different file format -- .unity3d. I need to extract and/or convert these files in order to be used in the newer Unity version. I do have access to a hard drive containing many versions of the original files, but the file organization is a mess, so it isn't obvious which folders are necessary.

I understand these files were never designed to be extracted (e.g. to prevent piracy) -- but I have found a few tools and threads online about potential processes/solutions: (Link1, Link2, Unity Assets Explorer, DevX Unity Unpacker, Unity Assets Bundle Extractor (UABE), Disunity experimental tools) Problem is that many of this information is years out of date by this point, has broken links, and/or references very specific Unity versions. Does anyone have any experience with doing something similar, and could help point me in the right direction?

Many thanks!

 

I recommend to upgrade in the smallest version increments possible. You can get all Unity versions from the https://unity3d.com/get-unity/download/archive and then pull your project through roughly each minor version, e.g. 3.4, 3.5 and so on. This way, Unity should handle all required upgrades automatically, at least I've upgraded a few projects from version 3 to 5 this way, never had to manually pull apart or convert anything.