Laid it out yet?
I've taken 2 1590N1-sized PCBs and tried to fit them in a 1590BB. They didn't fit.
Some narrower PCBs sort of almost fit, they went inside the enclosure, but then the adjacent knobs from one PCB to the other would be too close together on the face of the pedal.
If only the 1590BB was a smidge bigger, 132mm it would work for dual "1590N1" builds.
I'd say the K-mini and Pauper are "full-size" 1590N1 builds and you're best off with an XX:
1590N1 — 121 x 66 x 35 mm
1590BB — 118.6 x 93.5 x 30 mm (`1590BB2 is 34mm H)
1590XX — 145 x 121 x 35 mm
The Length of N1 perfectly matches the width of an XX while the latter's length accommodates the width of two N1s with some wiggle room.
While I'm at it here's a couple more, for good measure...
1590B2 — 112 x 60 x 34 mm
1590B3 — 116 x 77 x 34 mm
The B3 is great for adding an extra mod / control or two to a 1590B or 1590N1 build, but not duallies...
If you go to Hammond's website there are extremely helpful charts with all the sizes, making for easy comparison/planning.
Some hidden gems not oft used in pedal-building include 1590Q (square that matches the BB Length, and 1590Y — great for dual 1590A builds.