What about create 2 folders and each contain their own module version?
e.g.
- 2.x/
- hello 2.x module
- [ more 2.x modules here ]
- 3.x/
- hello 3.x module
- [ same modules than 2.x but 3.x version]
- This would make easier to compare same module for 2.x and 3.x versions.
- It also let us know clearly wich module hasn't been ported yet