Thanks, Roger. I think that the reason that I posted in the first place was that I wanted some reassurance that things weren't hopeless...

So, the unit is happily operating now. I applied the Mark 2 2.01 developer .upgrade file, and then used the Linux "download" utility to install the latest Hijack. Mark's Hijack page didn't make mention of the serial port argument to the download utility. It was only after invoking "download" without any arguments that I saw that a serial port could be added as a third argument. Very smooth process, once you know how.