Good catch. Looks like I got confused with the next one the seller posted on ebay that I'm watching, not sure where the card edge connector is on it, maybe right up against the case on the back: https://www.ebay.com/itm/222716933109 Maybe coming from same seller, this has a higher likelihood to be DD?
This was the one I got, AT88-S1: https://www.ebay.com/itm/222716613498
That is the almost the same drive as mine, but the add-on card is larger with more chips. This is likely the double density card rather than just a data separator like mine.
The end of the PCB sticking out the back left is for connecting slave drives, there are jumpers to configure and the terminator chip would have to be removed. This Percom drive doesn't have a printer port.
A manual is available on Atarimania. http://www.atarimani...rive_manual.pdf
On the AT88-A1 slave mechanism the card edge for the ribbon cable appears to be sticking out between the side and back panels, to the left of the fuse holder.