For jboss  HTTP port  see this file:
[jboss-dir]/server/default/deploy/jbossweb-tomcat55.sar/server.xml

Both simple http port(8080) and compressed ajp port(8009), is defined in
this file.
I know this uri looks a little bit strange, but this is because of JBoss's
architecture which is a JMX micro kernel, and every thing else(even web),
is deployed in the form of JMX MBeans. (see .sar extention).

Its not enough to change the HTTP port, u need to change a lot of
ports for run 2 jboss  instances in same mashin.
There's a preconfigured service in JBoss server/config-name/conf
directory that you can use to easily assign different ports to all
services in JBoss. Locate a ServiceBindingManager service in your
conf/jboss-service.xml file.

<mbean code="org.jboss.services.binding.ServiceBindingManager"
name="jboss.system:service=ServiceBindingManager">
<attribute name="ServerName">ports-01</attribute>
<attribute name="StoreURL">../docs/examples/binding-
manager/sample-bindings.xml</attribute>
<attribute name="StoreFactoryClassName">
org.jboss.services.binding.XMLServicesStoreFactory
</attribute>
</mbean>
This service points to a sample-bindings.xml file in the docs
directory that contains a sample of two separate port  configurations
for JBoss. By using the ServiceBindingManager all the port
configuration information in your server instance's configuration
files are overridden from this template. E.g. ports-01 configuration
for JBoss node 1 and ports-02 configuration for server node2.