Tap on it with a mini sledge in all directions for at least an hour. TAP on it, deliberately, but not like you are trying to knock it into next week or teach it a lesson it won't forget. The idea is for the brute tapping force to dislodge and break free the metals that are causing a tight interference fit. As mentioned before, whatever apparatus hangs down the well could be stuck within the casing too. i'd go get the biggest floor jack from menards/tractor supply/home depot/harbor freight that you can find. make a fulcrum on one side of it out of something that wont crush or move, like a car jack stand, then slide something that will not easily bend under that 90, like a car half shaft from a junkyard. Axles are pretty strong. put the floor jack under the car axle so the lifting force rides against the fulcrum, with the lifting energy of the floor jack driving hydraulic force up towards the sky. I recommend eye protection, a hard hat and welding gloves. While you are applying lifting force via the floor jack, It might be a good idea to cover the whole thing with that thick blanket that goes between a horse and the saddle, in case any of that metal breaks and goes flying, you will want it dampered and deflected from hitting you. Safety first. If the well hasn't been used in 25 years, it won't hurt to ensure you are doing things safely. I am not an expert but it looks like gravity and inertia are the things you should be looking out for. Gravity: if all the stuff below the cap is held by the cap and you break the fasteners loose, and your hand is in the wrong place at the wrong time, it will attempt to take you with it. Inertia: If you apply enough force to the cap from underneath and the metal breaks, it will go flying until slowed down by a horse blanket or a part of your body, or your dog, or the new window of your house. Think schrapnel.