I've used that site as well. It is best to have a specific need in mind and then focus on the file(s) that pertain to your need. It would take a while to download all of the files, but I can say that the links in the files work so, once you have them downloaded and in appropriate subdirectories, the files are self-referencing.
I did find a different site that had what was supposed to be a complete GS300/400 Service Manual for download in pdf format, but it was not complete and the links didn't work. It was less than $20, so I figured it was worth a shot. I requested, and received, a refund.