> How does it work for reproducing scientific experiments using legacy Python 2 code?
Install Python 2.7, which is by does with pip. Upgrade pip if you want, which will get you the last version of pip that supports Python 2 (the old versions haven't gone away, new versions just don't support py2 and won't show up when upgrading on py2). Install the needed scientific libraries. Run code.
> Are there legacy versions of these packages being maintained or at least preserved?
AFAIK, there is no plan to remove py2 packages from pyPI.
Install Python 2.7, which is by does with pip. Upgrade pip if you want, which will get you the last version of pip that supports Python 2 (the old versions haven't gone away, new versions just don't support py2 and won't show up when upgrading on py2). Install the needed scientific libraries. Run code.
> Are there legacy versions of these packages being maintained or at least preserved?
AFAIK, there is no plan to remove py2 packages from pyPI.