How about entering straight opcode, operand with only a hex keypad and two pairs of 7 segment LEDs. You can only see one set of numbers at a time. You had to write it out on paper to be able to keep track and count positions so you don’t use your spot.
I had to do this as a project in school. Two 8088 units that we breadboarded to a UART that we used to drive a fiber optic link to communicate with each other with a basic protocol. All descrete components hand wired and coded.
It made you tie all of skills together into a full system of hardware and software.