IEEE488 Cheese Wedge A
Here's the board, which has a number of departures from Acorn norms. First there isn't an Acorn marque at all, which isn't all that surprising, as the board is not made by Acorn at all, but by Intelligent Interfaces, and the serial number is written onto the board as well as the box.
The principal IC is a Texas Instruments TMS9914, an IEEE 488 controller.