Update: It's all working beautifully at the moment. My members all love it - they like it better than TWT's hack.
In fact, the number of queries has been slashed by 90%. Why? Because now when members use the shoutbox to chat, all they are refreshing is the new shoubox.php file in an iframe, rather than refreshing the previous TWT's shoutbox.php file which included headers etc. as well as 20 queries and a whole lot of other stuff.
Thanks for the nice port.

You can move this to the "Full Releases" once you update your install text files.