What you refer as"JBoss 7.1.4 which gets shipped with AEM"
==> Used AEM 6.5 windows installer with Turnkey option, and then selected JBoss as my app server, so installer installed jboss inside AEM directory, and when I checked in the JBoss admin console, it shows version 7.1.4 .. Make sense?
Upgrade procedure you are following
==> Installed stand-alone JBoss in a directory outside AEM directory, initially version 7.2.0 & then applied a patch on that to make it JBoss EAP 7.2.8 ... and then deployed AEM .ear files from the export directory inside AEM\ConfigManager folder. While deploying those .ear files, few are getting deployed successfully (adobe-livecycle-cq-author.ear, adobe-livecycle-native-jboss-x86_win32.ear, adobe-workspace-client.ear), but it's not deploying adobe-livecycle-jboss.ear file and throwing bunch of error messages.
Regarding the blog you have mentioned, I have followed almost similar steps - only difference is I have used the AEM installer first, and then grabbed the AEM .ear files from the export directory to deploy them in JBoss. I will try to see if I can find AEM .war file from Adobe site for version 6.5 as mentioned in that blog.