Inductive linear position sensors would be the most accurate (3 of them in a triangular manner):

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/linear_position_sensors/pivoting_slide/lri19-100r-00-20a

Photoelectric or Laser distance sensors with analog output for most accurate non contact sensing sensing.

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/photoelectric_sensors/distance_measuring_sensors/opt2011

Ultrasonic analog sensors for a cheaper but slower non contact method.

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/ultrasonic_proximity_sensors/18mm_tubular/uk6a-d2-0e

Or string potentiometers (or encoder) where the string retracts or extends with the table. You may be able to make these yourself for fairly cheap with some string, a pot or encoder, and a torsion spring on the shaft to keep tension on it wanting to retract. Some other places sell such premade devices but I cant think of any off the top of my head.

Or regular inductive sensors with analog output if you can be close enough and your table wont tip too far:

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/inductive_proximity_sensors/30mm_tubular/dw-as-509-m30-320

Also can be done with load cells though this is the most complicated, will have the least movement ability, and probably least accurate in the end for your situation due to their slow response times and cost. Probably would want to connect load cells between two springs which will lower their accuracy but increase how far the table can move, and you will also have to buy load cell amplifiers with the proper output to send to a PLC. The response time for this would probably be around 1 second for a decently stable reading of how far the table is tilting.

edit: or an inclination sensor also seems perfect for this and you may only need a single one of these sensors to do the entire job

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/inclination_sensors/gib-xy-015-a-2a

https://www.automationdirect.com/adc/shopping/catalog/sensors_-z-_encoders/inclination_sensors/gib-xy-045-a-2a

Feed any of those into the appropriate PLC module and set up a PID loop (or just manual jog moves) to make the steppers move based on the signal being fed in.