Yeah, that is the Getty's version which is the most functional one I have come across. They make them in three sizes and they consist of a solid block of aluminium that they machine in-house. Somewhere I have better images and will put them up (unless Kevin Marshall or Mike Mitchell beat me to it!)

Here are a couple of other versions as well.

adj install hrdwre sized.jpg

adj eye bolt_sized.jpg

Some folks may tend to say "Well if you know how to use a level then you don't need things like that". I would respond by saying. "Exactly what do you intend to "level" anyway?
Many old world frames tend to be very irregular in their construction. "Level" is a highly subjective, aesthetic condition the reality of which can be greatly assisted by the tweekability of adjustable hardware!
I would be curious to see other versions of this kind of hardware and where folks could purchase them.