This is a vintage Nikko Dictator replacement motor mount (for 380/390 motor). In order to accommodate longer motors, this mount does not come with the structure for a back cover.
upgradeparts-nikkorc-dictator-motormount
This version provides for a slightly larger hole for the pinion to pass through in case you have difficulty removing the pinion from the motor shaft (you should know what I mean if you have a hard time removing and replacing the pinion):
upgradeparts-nikkorc-dictator-motormount-largerhole
In any case we recommend that you use PETG or ABS. PLA is not strong enough for this particular application.
If you want to abandon the motor entirely (run the car as a 2WD instead), use this cover mount:
