As you've probably figured out, my computer is now fixed. Thanks go to Don and Dave and a few others who gave me some advice about the various Sun models. I decided to pick up another Ultra 2 and use the parts to fix my machine. Worked out nice and cheap and now I have a selection of spares for the future.
Bob, I've been meaning to e-mail you about the phase convertor project but haven't got round to it yet. I'll be in touch soon.