For this level you have to essentially create a four byte random access memory (RAM) in a confined space.
First you need four 8-bit registers to store and retrieve the bytes independently.
Link all save value pins with the input and all output pins with the output.
Connect the load pin to the enable pin of the output.
Next build a 2-bit decoder to activate one of the registers at a time.
Lastly use eight switches to build two busses that actuate the load and save pins of the registers and hook them up to the corresponding inputs.
Connect the switch pairs to the respective decoder outputs and you're done!
