Wider Duender motor mounts for 4040 y axis

If you find yourself wanting to build a Duender with MGN9 rails and 4040 y extrusions, but instead of running the MGN9 y rails in the inner v-slot you need them to run in the outer v-slot, these mounts are for you.

Build the frame as per the stock Duender build, but with 4040 extrusions half overhanging the sides of the frame. These mounts will keep the motors in the stock position and also keep all of the stock mounting points (into the end of the 2020 cross brace, into the rear face of the 2020 cross brace, and into the lower inner corner of the end of the 4040 y rail). Instead of the front-to-rear beltpath aligning with the inner v-slot of the 4040, these mounts have it aligning with the outer slot so that the y rails can be mounted further apart.

Note that mounting the rails this way won't increase the x travel of the Duender, it just allows for a longer x axis extrusion than stock. You will still have to determine for yourself how you'll sort out endstops, if you're using them.

I extended the motor mounts by 20mm; this keeps the motor in the stock Duender location, but shifts the outer bearing stack from being aligned with the slot on a 2040 y extrusion (or the inner slot of a 4040 y extrusion) to instead be aligned with the outer slot on a 4040 y extrusion.