It took me a good 40 minutes and a part of my fingernail, but I managed to abuse a standard NEMA17 mount to fit M5 bolts at the spacing required for the carriage, using a handdrill, pliers and a screwdriver.

 Installed it

And the first extruder is in place... Now I still need to figure out where to install the BLTouch. Probably going to mount an L bracket between the motor and the extruder. <-- scrap that...

4 tie wraps + 2 pieces of a wooden fork as a spacer. That BLTouch is going nowhere...