I'm no 3D Design expert but this allows Oled, Rotary Socket and USB port to be neatly fitted into one of the Cartridge slots in an Acorn Master. This utilises a USB connector that is premounted on a circuit board as supplied with Piotr's Mini Gotek kit.
The holder simply slots into place - Since the pictures I have added a standoff to allow connected cables to be cabled tied to prevent them being pulled off the board.
Unclipping the bezel will allow the whole unit to drop through the slot so you dont need to disconnect any wires.
Really needs a better holder for the OLED (This uses hot glue) perhaps a clip mechanism so feel free to remix at will - The sizes are pretty much spot on though and fits securely in a spare slot.