How do you change the back 3 plugs on a 1989 Oldsmobile Cutlass Supreme?

Yes he is right about moving the engine. Only block the wheels and put trans in neutral so not to damage trans.

To access the three spark plugs in the back of the engine, you must remove the two bolts in the 2 torque struts on the front of the engine. Then, using the top loop mount, rock the engine forward and lock in place with the torque struts in their lower bolt holes. Afterwards, rock the engine back to original position and insert torque strut bolts in their original position.

On my '91 Cutlass, with the 3.1L, the easiest way I found to change the back three spark plugs was to remove the serpentine belt and then remove the alternator. Then had all the space I needed to change the plugs.