I dusted off the darwin, tightened the bolts, and rubbed the rust spots off the rails (stored in the garage - not good!). A couple of the acrylic joints had cracked, and a couple of the cross-bracing rods had come off. I tided and reaffixed as best I can. I spent yesterday and today re-plugging the gen2 stepper driver boards into my gen3/Arduino mega setup, and then fixing the firmware for my custom setup.
While uploading the firmware, I was getting a lot of errors -
Binary sketch size: 28098 bytes (of a 126976 byte maximum) avrdude: stk500_paged_load(): (a) protocol error, expect=0x14, resp=0xa7 avrdude: stk500_cmd(): programmer is out of sync
Although the upload still *seemed* to work, it was a little worrying. Occasionally, it would work OK, but almost every upload would report this error.
Checking the internet, one post mentioned interrupts causing problems. I know that interrupts are used in the firmware for stepper timing and extruder heater control. I found that if I uploaded the 'blink' sketch first (nice, short quick sketch) and then the firmware, it uploads successfully without any errors!