according to http://opensees.berkeley.edu/OpenSees/developer/svn.php there's a way to obtain an actual svn checkout for OpenSees v2.4.3, so there's no need for datestamping:

```bash
svn co -r 5621 svn://opensees.berkeley.edu/usr/local/svn/OpenSees/trunk OpenSees
tar cfvz OpenSees-2.4.3.tar.gz OpenSees
```

so, switch to simply using:

```python
sources = [SOURCE_TAR_GZ]
```