IEEE488
Adapter
Here is a close up picture of the circuitry inside this most puzzling of adapters.
There is no Acorn marque on the circuit board, the serial number does not confirm to the usual Acorn conventions and even the way the ribbon cable and clamp fit to the PCB is not what we would usually expect from an Acorn-manufactured unit.
However, it is a genuine Acorn unit as can be seen by comparing it to the Acorn Cheese Wedge version here.