Upper A-arms don't move?

I am in the process of upgrading to LS1 brakes and I removed all 3 castle nuts from the driver side knuckle, but I am having problems pulling out the knuckle because the upper A-arm won't move at all! Any ideas???
I did an engine swap through the bottom last fall. Could I have screwed something up in the process?
Thanks!

At the local Harbor Freight I picked up a ball joint "puller". Works great and only costs $8. Sears sells them too for twice the price. There are 2 sizes: the smaller one should work on the upper ball joint.

Whacking the upright with a big hammer while holding a big hammer behind it usually pops it free.

Jon,
can you explain that again? Where do I put the other hammer? So just get a big hammer and hit it upright until it brakes loose? I tried that although the hammer wasn't that big... I'll give that a try, hope won't bend the arm.
Thanks.

You need to hit the side of the knuckle where the ball joint goes through it. Have someone pulling up on a big pry bar to keep pressure up on the upper control arm. Dont acually hit the upper arm, that wont get you anywhere

Tapping the upper ball joint stud can also help-that's how I did mine. If none of that works it's fork time.

Put the castle nuts back on, but only screw them half way. You don't want the knuckle to just fall off onto your foot. Do the upper first. Give the ball joint screw thingie a good solid upward whack with a hammer and it should come apart. Then suport the lower control arm with a spare jack or something, then whack the bottom ball joints loose the same way. Just be careful about not screwing up the threads on the ball joint.