... all 4 bj's, upper & lower, right & left ... ALL C3 vette bj's have a tapered stud that press fits into a tapered hole in spindle/knuckle. A key to this procedure is understanding that (even when the wheels are off the ground) the front coil spring is compressed and has a lot of stored potential energy. First, get the car up & firmly & safely supported on at least 4 GOOD jackstands (I like 6). Approach only one side (passenger or driver) at a time. Next, remove the brake caliper and knock the tie rod end loose from the spindle/knuckle with a pickle fork. Loosen the nuts on both lower & upper bj's ... ONLY LOOSEN ... DO LEAVE ABOUT 3 THREADS FULLY ENGAGED. Then knock the pickle fork into upper bj... it will pop loose the press/interference fit, separating from knuckle/spindle ... BUT the nut will hold it from coming completely apart. Now, do the same thing to the lower bj. Now, put a floor jack under the lower a arm near the lower shock mount and put a little upward pressure on the LAA. Now, remove BOTH lower & upper bj NUTS. Now, SLOWLY release the pressure from the floor jack. As the front coil spring extends, the bj's will pull apart & free from the spindle/knuckle.
I don't know how you snapped off the end ? never heard of that happening. The taper just pops and it is off. Some guys just beat on the stud with a heavy hammer and it pops out of the spindle. Anyways when you got the new ball joint in place it doesn't take much to tighten with the nut and it is done. You can't pull the taper further and further, it just seats and snug it up. The nut usually lines up the slots with the hole so the cotter pin goes through, so no way you can overtighten and go too far.