After quite a while, with a broken metacarpal and the recovery that came with it, I was finally able to finish this build, so here I am reporting back on it as promised.
I ran into a few complications, basically due to distractions during assembly, and spent a good while troubleshooting, but luckily I was able to solve it — it works well and I'm very happy with the sound and functionality of this pedal.
The main thing is that I managed to fit the complete circuit into the 1590BB2 enclosure, so I can confirm it's doable, although I'd definitely recommend using the correct enclosure specified in the build documentation if you have the option (I didn't — couldn't find one available in my country).
In case you find yourself in the same situation, the 3 problem points for the reduced depth of the 1590BB2 are:
The footswitch PCB electrolytic capacitors (which you can solder upside down without any issue, as was recommended here previously).
The height of the lightshield (in my case I cut the sides down to reduce the total height to the maximum point allowed by the height of the lamp itself. I had to leave out the lightshield's little cover and used aluminum tape in its place instead.
The position of the jacks can complicate fitting the enclosure lid. The lip of the lid touches the plastic housing of the jacks. It's very hard to measure in advance the correct point to drill and position them without being able to confirm exactly what height the PCB and its components will end up at once soldered to the potentiometers; but in my case I solved it by adding washers as spacers from the inside so the plastic housing sits one or two millimeters farther from the enclosure's aluminum wall and closes properly.
I love being able to switch between the different rates with the footswitch. It gives some nice expressive possibilities.
Here's a short sample of how it sounds with a short Boss BD-2-style analog delay before the Straylight.