This post was made from behind a proxy server at work. If the XML-RPC call to radio.helloWorld works you will see a sensible result below:

<result>
Hello Duncan, you're using your loopback address 127.0.01 on port 5335 in this XML-RPC call!
</result>

Cool! The slight mods I made to system.verbs.builtins.tcp.httpClient seem to have done the trick. The mods (in emphasis) were:

bundle { //see if it's the same machine
	if string.lower (server) == "localhost" or server == "127.0.0.1" {
		flSameMachine = true}
	else {
		try {flSameMachine = tcp.equalNames (server, myAddress)}}; //DW 3/9/98
	
	if port != user.inetd.config.http.port and port != user.inetd.config.http2.port {
		flSameMachine = false}
	else {
		if not (inetd.isDaemonRunning (@user.inetd.config.http) or inetd.isDaemonRunning (@user.inetd.config.http2)) {
			flSameMachine = false}}}

Please note some of the original comments have been deleted just to keep the pre-formatted column width down.