That's my website, and I decided to give up versioning the model installs when the new version of REFLEX came out. It would be too complicated for me to maintain more and more model versions for different REFLEX versions.
Even more important, REFLEX withdrew the 5.03 download so at least now it's illegal to offer this version for download. I don't think you'll find it anymore. But maybe I'm wrong and someone has it, and you can download lots of models and sceneries for the old version here at RC-Sim.
I just don't think it's worth it. You're fixating on a more than 13 years old version, and you would feel like that when you would get and see it.