With Support: These models have a little support material added and a bridge for the mounting holes, which makes it possible to print the model entirely without additional supports.
With Cutout: Our PTO hole (replacement frame part from Britpart) had quite a thick weld bead for which I added a cutout in the model. Your frame may vary, so you can use the model without cutout. Furthermore, you can use the “Cutout Piece” to place a negative volume in PrusaSlicer and create a cutout in your desired spot. The model has the cutout at ~18° relative to the horizontal axis.
Recommended Material & Print Settings
The print in the pictures was made with ABS, in a car it's best to use ABS, PETG, ASA, …
Use high infill in the tabs for a strong part. The disc part can have less infill.
3 perimeters recommended
Additional Hardware
Trailer Socket Herth+Buss 51305036 (or equivalent, most 13-pin sockets share the same bolt pattern)
3x M6 hex key bolts and nuts (length depends on your specific socket)
3x screws for mounting the adapter plate to the frame (self tappers, rivnuts, tapping directly into the frame, …)
Please consider liking the model and posting a Make. It took a lot of revisions and a lot of filament and O-rings to get this right.