Blender, 2.6 and 2.7, has somewhere changed to using Python 3 instead of 2.6/7 if i’m not mistaken. Python code for Blender is what needs to be rewritten to work on Python 3 and i am not sure about underlying Python to C stuff. So that there is a ton of work to rewrite python (and maybe even C parts) code to start thinking about compiling 2.4 and making it to use Python 2.7. All addons are using old-fashioned python code. These need to be checked for incompatibilities. Print is easiest to fix, there are more on the list.
blend files are backwards compatible ofc (checkmark Legacy on T panel).
It was comparatively easy to use Blender 2.49b one or two years back on linux Ubuntu or Mint; now, when they are using Python 3 on the system level it feels much more complicated to set working Python 2.6 just for running Blender 2.49b. Last i managed get functional complains that there is no Python and scripts wont function.
I’d rather make some USB stick with some older OS, Python and Blender 2.49 happily running - you would need that only for import export functions, no fancy screen modes, no speed needed. Then either boot this or use on virtual box. in parallel, on top of your real OS.