The two Chinon FB-354 floppy drives on my Amiga 2000 have six pins at the back between the data header and the power header. The one Chinon FB-354 on my 2500 has the same six pins but has a jumper in a different location:

A2000 both drives: A2500 single drive

o o o o o o

o --- --- o

I don't know what the difference signifies or whether it is important.

Each machine has the same 34-wire flat ribbon cable with the same twist.

Thanks for your replies.