What is the complete part number of the 1394 system? It may have RIO comms in addition to those already mentioned.
And you'll want GML Commander v4.03 in order to communicate with it. The part number is GML-C-C. I am not sure if it can still be purchased, but I could not find it on the website. You should try to call your AB distributor and ask.
Depending on how the orignal program was written and how the serial port is configured, you may be able to learn a lot just from the terminal interface...if they used "print" blocks wisely in the code.