Hard to say what it needs. I see a body lift and no visible body mounts in the picture. This originally had four body mounts across the back. Would need to know the condition of the hinges. Any play in the hinges should be resolved first. What condition is the rear sill in. Rusted or poorly repaired sill will flex. With the tube spare tire carrier that started with the 77 model the carrier used the sill not the door to stabilize the carrier. If I had issues would modify the earlier plate carrier to do the same thing. Have a couple early FJ40s with rusted sills that the tub is buckling under the weight of the hard time. Have four cruisers in the 68-76 range that tire carrier are rock solid.
When I ran a ‘76 carrier on Ruftoys (same design, driver’s side) I added a vertical tab on both ends of the top of the plate, drilled the one closer to the hinge, and made a drawbar across the back to the other carrier. That helped keep the plate from flexing without having to do something extreme like drill through the tailgate.