The information is still there but it appears the new browsers don't understand the links. To get down to the next level (the model year) for models 2006-2011, the link is of the form
http://www.gmb.be/CJD_parts/CD5/Catalogs/06-09/Index11.pdf
That is .../CJD_parts/CD5/Catalogs/06-09/Index11.pdf
Replace the "11" with "06", "07", etc for model years 06-10
At that level, you can see the available model codes. To get down to the next level, the pdf you want to see, it looks like
http://www.gmb.be/CJD_parts/CD5/Catalogs/06-09/11D2.pdf
This would be for a 2011 Regular & Quad Cab 3500 (D2)
For other years and models, replace the "11" with the 2-digit model year and the "D2" with the correct vehicle code
I did not try all this with the earlier model years. Those links may be similar or may be different. I had a time trying to figure this out on a Mac: opening the web page PDFs in Preview, clicking on the links (which failed but gave me the info I needed), then testing the links in Safari. Someone who has a browser that will open the links correctly should be able to easily fill in the rest.
Now, if anyone has a link to similar pdfs for 2014, I'd love to have it.