The main problem I am having at the minute is the one bit delay between RX -> TX messages. As if I use the standard serial port the minimum delay is one byte, which if there are many nodes on the network makes full ring comms quite slow.

Install an external switch that connect Tx and Rx. You will still read what comes down the tube. If intervention is required, open the switch (you have 1/2 bit time get ready to do so) and use Rx to Tx Through the uC.

Erik