Neither of these arms is the shape of the one on my old van. It was almost but not quite straight, but leaned over more towards the slave. You are on to something when you mention the alignment of the ball and arm. They are just not making these parts correctly any more! Hence lots of misery, and forum threads.
I think the original arm was forged, but it should be possible to replace it with a welded fabrication. Like many things on a Mini, there is an opportunity for someone to undertake small scale production of well engineered replacements.
There is also an opportunity for someone to develop a direct acting slave kit, as fitted to modern cars. It would need a modified wok, but the piston and cylinder would not need to be annular as there is no shaft to pass through the middle. A typical brake calliper piston would be about the right diameter to get suitable stroke and force, and if running in a bore with the same type of seal as a calliper would also be self-adjusting.