Discovered that Factfinder only provides access to SFT1A and not SFT1B. I was not previously aware of this. STF1A provides population counts to the blockgroup, while STF1B provides down to the block level. Dropped by to see our Gov Docs Librarian, who told me that we only maintain the STF1B disk for Texas. Good grief.
Then I discovered that the UC Berkeley Social Science and Government Data Library provides an easy
So, there I am feeling happy for a moment. Just a moment, however, because then I remembered that those old ArcView 3.3 Data & Map Disks contained this data. Sure enough, disks 4 & 5 contained 1990 block centroids with the attribute 'Pop100'. I haven't thought about these disks in quite a while.
Well, let me tell you I am right now in the process of creating metadata and these files will be uploaded to our servers ASAP.