Managed to get the disk drive working this evening. I'm not very good at waiting, so I went ahead and ordered the edge connector needed to make my own IEEE-488 cable. If/when I get a proper cable I can always use the connector to make a cbmlink cable for the user port. Anyway, it arrived in the post today and after a bit of soldering on one end and crimping on the other, I was all set.
First disk format didn't quite turn out right - loading the directory listing I got nothing but a 0 and a double quote in reverse video. Formatted again and it looks like we're in business! I wrote the obligatory "hello world" program and it saved it OK. Weird thing is, of I load it back (even after a "new") the listing still contains the directory information. That can't be right, can it?
Also had a bit of "machine gunning" at the start of the format. I say machine gunning; it was more like a loud fart really ;-) During some operations the centre LED starts switching from green to red pretty rapidly. Either of those things anything to worry about?
Oh, and it looks like drive 1 (I'm assuming that'd be device 9?) doesn't work yet. The format command exits immediately without any kind of error message, but if you try a LOAD the PET reports it's found the program and tries to load it regardless! No activity at the drive though... something to look into.
Update: Nevermind that last bit - both drives are of course device 8 but you need to specify the drive number!