I’ve made up a couple of Polargraph SD prototypes following this same kind of pattern. They are very simple.

It uses a Mega protoshield (a cheap source of which I am yet to find), an Adafruit micro-sd breakout board, and the motor driver shield of your choice.

Why yes, there is room on that protoshield to build a full motorshield itself! Hm!

The wiring itself is just a slightly neater version of this