[joedoh]

do not die grind the ball joint.

there are a couple of approaches:

you can install an upper ball joint with more travel, if available. it may not get you all you need.

you can pie cut the uppers on the vertical just inboard of the balljoint, cut a pie shaped piece out on front and back of the arm, then jack up the lower again. the upper balljoint will bind and the arm will bend, closing the pie cuts, which you weld back up. the drawback here is that you will lose exactly as much lift as drop you gained, which may not matter to you at all.

you can raise the entire upper control arm up at its mounting. this will make the unequal length arms have less camber change and may give you the extra drop you need. the drawback is the arms will be closer to steering components and exhaust headers etc.

you can buy drop spindles and or custom lower arms with drop geometry. this wont keep the balljoint from binding but it will give you more drop before it happens.