So, I am sure everyone her is DYING to figure out what happened. Kidding, I am sure most of you have forgotten.
But, to add to the internet base of knowledge, I figured out the problem.
I bought a new set of calipers that are digital and more accurate and re-measured everything. Turns out, the crown race seat on the fork is 27mm, not 26.4 and is therefore the crux of the issue. The top and bottom cups are 30.2, so normal ISO there and the threads are 1"x24tpi, so also normal.
The entire headset is ISO normal except the crown race, which is 27mm. I slipped the original on with a PVC pipe with absolutely no issue. The frame and fork are happily re-married using the original headset. I wanted to use a modern sealed bearing headset because they are way easier to deal with, but it looks like for this one, it's the original or nothing.
Thanks for everyone's help.