Author here for your 8087 questions. I find adders and ALUs interesting because they are key to the performance of a system and every system implements them differently.
The reason you don't use prefix adders in 1980 is that you can't possibly route them because you don't have enough metal. So instead, you use chunks of Manchester carry chain because the "tapping internal nodes" that everybody cites allows you to route nodes in diffusion and polysilicon instead of having to use metal.
Of course, THAT only works because you have 5V (or more) and can connect lots of transistors in series and still have them work. As your voltage falls you can't connect as many transistors in series, so you switch to architectures that prefer active gates over passthroughs and long chains.
So, as your available metal layers, supply voltage, transistor speed, threshold voltages, capacitive load and power dissipation all shift over the engineering landscape, your "optimization" shifts with it.
But if you duplicate all your slices, you can have the results for both carry = 0 and carry = 1 inputs. Then just switch which one is correct - total time 1 add plus N-1 switches.
Just for double (and change) the hardware. Cheap.
I've been curious about transistor counts for floating point units for a while, but it's hard to find information about them.
How does the clocking work exactly? The circuit is fed A and B and up down up down clock and then the output appears? How does the consumer (circuit) know when to read the result? Is there a "result is ready" flag? How long does the result stay stable? One full clock cycle? So many questions...
There is some complicated timing within a clock cycle with slightly delayed clocks and whatnot, for instance, to precharge the carry lines at the beginning of the operation. The 8087 is mostly synchronous with the clock, but they "cheat" in many places.