This may seem like a stupid question, but you were able to loosen the clamp on the needle bar okay? Is it accessed through a hold from the blind side? Of course, I'm sure you did, but just in case
One thing I did one time on a very stuck one, was fashion a bit of a jack screw under the needle arm. I used a bolt with a large flat head, a hex connector, and another bolt on top and a jam nut, I think between the hex connector and one of the bolts, to make it rigid. I put a piece of wood under the jack screw, and a piece of aluminum on top, and using a pair of open end wrenches and about 5 hands, heat, oil, and magic spells, was able to get it to budge upwards a bit. Then I used something I won't go into to able a little downward pressure. Good luck with that!