A number of them are only links to the articles on other sites (such as a few of your own articles but if you prefer i'll be glad to pull the links down if you don't wish me to link to your articles)
which unless I'm mistaken would be considered public domain if the info is posted in a thread for anyone to see and of course proper credit is given to the original poster or author of the information.
The copyright you are violating is not John's. You've have posted .pdfs of the actual magazine pages and that's copyrighted by the publisher, Amos Automotive Publishing. While John may have given you permission to use his text, what he couldn't grant you is permission to repost the magazine's pages.
Links are not copyright violations. What's a violation is reposting the actual magazine pages or posting of an author's text on your site without permission from the copyright owner. You have a ton of CE's copyrighted material on your site. I personally, have not stake in that but the magazine publisher may feel it's copyright is being violated. The proper thing to do is contact Amos Automotive Publishing and ask for permission to reproduce pages out of "Corvette Enthuaist" for your web site.