Use two long Rigidbot extruder 45x3mm bolts to mount the root stand to the aluminum plate. Use two 25x3mm bolts to mount the clamp to the root and through the root to the stepper. Use two e3d fan screws to hold the fan onto the clamp face.
Technical
-2 45x3mm hex head bolts (reuse RB)
-1 25x3mm hex head bolt (reuse RB)
-1 25x3mm hex head bolt (supply yourself)