I finally got time to assemble the ALU PCB, after having been away for 6 weeks, waiting for components to arrive, then dealing with the start of the lockdown.

Overall, I'm pretty happy with the result. I had a few problems:

• I ordered the wrong size of component for all the single-gate chips, ordering the smaller SOT353 ones instead of the SOT753/TSOP5 footprint that I'd designed the PCB for. I managed to re-order the correct size of almost everything, but couldn't find TSOP5 single-gate AND chips anywhere. Fortunately, I only used two of those, so some gentle bending of the legs of the smaller chips did the job, though it's messy (see component U108 in the close-up photo above).
• I screwed up the logic for disabling the adder/logical output if the shifter is enabled, so if you use SLL, SRL or SRA operations then both the shift unit and the adder/logical unit attempt to drive the bus. This is generally Not Good. I'm going to have to bodge in a fix for this for now with some sky-wired components, until I can re-spin a rev2 of the board.
• I also still need to tie down the floating inputs on the comparator ICs, since it looks like the less-than line isn't working correctly.