Thanks M. B. Doc

Ball joint replacement is done, but not without help. I ended up taking off the knuckle assembly and having a machine shop press in the new ball joint.

DIY Lessons learned:
1) The base plate is not to be used to pull in the ball joint or the threads will get stripped.
2) Machine shop can extract the old joint and press in the new joint without having to get to the other side of the knuckle assembly, so the parking brake assembly and disc cover could possibly be left alone (I took the parking brake assembly completely off - not sure about cable attachment if left on).
3) An alternative to fitting a stubby hex key wrench in the cramped space above the joint is to remove the rubber dust cover and clamp a vice down on the middle of the joint.
4) There was a Torx T45 size slot at the top of the new ball joint bolt. In order to get something to fit up there I had to cut off approx. 1/4" of a T45 bit. I held the ball joint bolt steady with a 5/16" box end wrench holding the T45 bit and screwing on the nut with a 21 mm open end wrench.