Unless you are experience at editing the config.txt file, this is a bad idea. Most Pre-SP3 content requires edits just to get it to show up in Trainz and then even more edits to get it to work. But it can be done.
As for downloading, Pre-SP3 content did not come in a CDP format. It was .exe files. Much like a zip file. That is why it doesn't work with download helper or CMP.
William