Austin, just try to move to JBoss3.2.5 (embedded tomcat5.0.26). Use mod_jk1.2.6 related connector. These are the recommended versions. See if you can spend your efforts in achieving the upgrade rather than making older versions talk to each other. :-)
Unfortunately, due to a customers demands and the reliance on third party software that is not yet compatible with newer versions of JBoss upgrading all of JBoss is not an option.
The fix is to upgrade the version of Jetty packaged within JBoss 3.0.7.
To do this, simply replace the org.mortbay.jetty.jar file in the jbossweb.sar with the org.mortbay.jetty.jar file of the version of Jetty you want to upgrade to.
The relevant fix for AJP13 issues is in Jetty 4.2.11