Page 16 of the Build Blog shows a bit of the blow-by-blow, but basically, virtually all the damage occurred right at the "step" where the collet end bell flares out from the rest of the spindle shaft.
The total bend was fairly minimal- about .008" TIR- so rather than try and somehow bend it back (and possibly cause more damage* I elected to just turn it on the lathe back to round.
The screwup I did was I misinstalled the shiny new super-precision ABEC-7 bearings. They're angular contact, and in this case need to be installed specifically so the load goes toward the... well, load-bearing side.
I duplicated the way the old bearings were installed, which as it turns out, had also been misinstalled. When the center locking collar was snugged down, it tried to pull the center races of each bearing out of the outer race- that particular direction (towards each other) was the non load bearing direction, and it took actually minimal effort to pull the inner races out of the outers.
I didn't "destroy" them- actually, they still look perfect, and I was able to reassemble and clean them- but I'm quite certain I did enough damage to ruin the "super precision" rating. They're probably still much more accurate than a typical truck or trailer bearing, but they're also almost certainly no longer ABEC-7.
I went ahead and ordered a second set, but in the meantime, as I said, I was able to reassemble these and install them, so I could finish tweaking the spindle and trying it out.
But, it boiled down to my unfamiliarity with this kind of angular-contact bearing, and the fact the ones I was trying to use as a reference were also installed wrong.