In this case it is not necessary for the uP or the uC to be capable of executing all its instructions or to contain all its features.
It is sufficient if the uP/uC can execute the following sequence:

LOAD operand --> register
ADD operand1, operand2
STORE result --> memory


This assignment is more complex than others because it involves design decision (how to implement the control unit of the uP), and it is also a bit more difficult to debug (than, e.g., the arithmetic algorithm, where the intermediate results can be used for debugging).
The students who chose this topics are advised to start from a real uP or uC and to discuss with the teacher what features have to be implemented and what features can be ignored.
Also, the students are advised to allocate enough time for debugging !!!