My 1st post on here in ages, and just to say this.....................................
this thread gets the JuvUK seal of approval
nice work
Thank you kind sir

I've another little update this evening...
I cabled in the HxC to make sure everything is working - I've connected the DVDROM here loosely as otherwise it takes ages for the IDE to timeout before booting (Edit: Interestingly, the drive I later used instead of this one still had that issue, fixed by a ROM patch)
The long and short of it is that both drives show up and work great too
If I throw the switch on the floppy cable (with the power off of course), the drives do indeed swap, so the HxC can be either DF1: or DF0: and the internal FZ-357A the opposite. Chuffed

I need to do a little work on the settings of the HxC, but otherwise it's golden.
One thing this did make clear though, was that I've mounted the SCSI2SD in the wrong place... So I'll be scraping that off again tomorrow and remounting it closer to the DVDROM mounts. I can't access the last partition on the SCSI2SD at the moment; I've a feeling that WinUAE has used an area of the SD card that it shouldn't have, making it unreachable. I'll try to start sorting that tomorrow. Edit: Sorted that now, WinUAE had put the end of the partition right at the end of the SDCard which is not accessible by the SCSI2SD. Did some other tidying such as killing off the scsi.device patch that is no-longer required too - boots _very_ fast now.
I knocked up a set of extension cables for the HxC this evening also though - hopefully it'll be a doddle to mount in the new case when it finally arrives!