To get rigid bodies to follow the texture and move in a curved fashion, I used an Area with a box shape collider to track objects on the belt. I had to set the area's space-override property to "combine-replace" to keep objects from accelerating. The area seemed to mainly override gravity, but I needed a constant push on the objects instead of acceleration.
During the area's physics process:
1. For each rigid body found in the area:
2. Find vector v from the conveyor's inner corner to the object.
3. Find the clockwise pointing tangent r vector from v.
4. Normalize r and multiply by belt speed.
5. Subtract from r the body's linear velocity. (to prevent acceleration)
6. Save the force to the body with the intended speed.
To prevent the object "popping" in speed when getting pushed by multiple conveyors, it only calls add_central_force with force f once per physics process.
Once used, f is reset to 0,0,0.
On adding a new force from a conveyor:
1. Set f to the new force if f is all zeros, else:
2. Ignore the new force if it is equal to f, else:
3. Add the forces together, normalize them, and multiply by the intended speed.
This worked out just fine and rigid bodies are pushed around the corners very smoothly. I mainly am posting all this in case someone down the line is curious, and in case my logic throws up red flags to a more experienced developer. 
