I finished construction on the 'reference multiplexer' here it is:

the image is inexplicably upside down (again)

Basically this takes in the the ROM data bus and switches it between the bank of LEDs and the rest of the computer. There is a tact switch that determines controls the address bit on the multiplexer. This multiplexer is necessary because it allows me to ensure that the ROM is outputting the correct values, without having it hooked up to the rest of the computer. The next piece to build is a 1:16 (de)multiplexer with the input held high. It will perform the functions of the control logic. This final multiplexer is supposedly the last piece of the computer left to build, so barring any major flaws in the sequential logic, the computer should be able to run a program.