Hi
Mine sure is a HD floppy, maybe wrong labeled, I'ts was a spare for my A4K if the actually broke (I hope no). I've been using for a time in the A4k and working fine with 1.76 Mb disks, checked: it has switch for "HD" disks marked on the PBC too.
It has only one rear jumper to change to DS0 or DS1, the jumpers you say no. Maybe I must open it to see it?