Yesterday I finished wiring up and debugging the 74181. The wiring of the second half is fairly disorganized, mostly because I wanted to try to fit everything on two more boards. It was also difficult to organize the logic by function, so the ICs are unlabeled. It's mostly AND gates, with a few OR, XOR, and inverters thrown in.
Here it is pictured next to an actual 74HC181:
Since this is a 4-bit ALU, if I wanted to use this logic in the computer project I'd need to build 2! That would make the ALU nearly as complicated as my first 8-bit computer in its entirety.
Now that I've built this model of the 74181, it'll probably go on a shelf and I'll use the actual 74HC181 IC in the computer project. I'm considering this sub-project a success and I'll assemble the ALU for the new computer next.