You lining has bonded to the drum. No amount of any penetrant will help. Option 1 is that you can make a sort of planishing hammer by welding a 1" cube of steel (bar stock) to a punch bit for an air chisel. (air hammer) Cut off the punch where the taper begins and weld the bar stock to it. Have someone apply a goodly amount of rotational force by using a prybar between the studs. While under pressure, rap that sucker with that air hammer around the entire circumference, working back and forth across the width as you go. After a full circle, apply rotational force in the opposite direction and repeat. If you like, you can grind the head to fit the grooves of the drum.
Option 2 is to use heat while applying the rotational force. Try to heat it as evenly as possible using a cutting torch. (without hitting the torch lever!) If you've soaked it with penetrants, they will billow and likely catch fire, but keep going. It won't burn long, but I highly recommend wearing a respirator when you do this. Try not to create any hot spots or make it glow red at any point. Do NOT try to quench it or cool it. Sometimes it will come loose after you allow it to come back to room temperature. Usually, the expansion of the drum will break the bond, but sometimes it works better when allowed to come back to ambient temperature.
Last option is to cut the hold-down pins on the backing plate and pry starting from the bottom. Make little wedges to get in your first gap and slowly work upwards, applying more wedges as you go.
All options take a lot of time. There's no quick way.
