What is up with the UCA?

If you actually compared a left, and a right, UCA side by side, you will find that they have an "angle" to them, depending on which side of the vehicle they are installed on.
That's perfectly normal.
I really don't know why the right one in your picture is pretty much flat.
There is no difference in the the UCA between any of the 73-76 A body line of cars.
So one of them being from a different model, or year is out of the question.
The only thing that comes to mind in getting one "flat" like that, is some unknowledgable person tried to press out a ball joint, instead of screwing it out, and it got "tweaked" under tons of pressure in the hydraulic press.
But i don't know. Only a guess.
I just happened to have a set of A body UCA's out in the garage that i took pictures of, for my next round of eBay sales, so here's a front,side by side picture of what they normally look like.
Hope it might be of help to you.
Jim V.

Oh, i forgot to mention, the numbers on your UCA, are the year and day code that they were manufactured.
The first number 4, is the year, and the other other numbers are sequential day of the year they were manufactured.
So your UCA's are off a 74, and were made pretty much close to one another, in the days.