Its a spool type pitless like a Baker Monitor standard.....most that I've seen on wells less than 8" do not have any sort of lock mechanism, they simply rely on gravity to seat the spool. It so badly corroded, I bet that is your problem pulling. We pulled one few months ago that was very corroded....the weight of the pump assembly was 5800#, and it took over 13000# on the crane to unseat it. Also, this type can be much harder to pull if you aren't pulling straight, which you probably weren't if you were using some sort of jack. Pull straight and pull harder, use a good pull pipe and screw it in very tight.