Happy to report that the problem looks to be corrected. With some minor massaging, I got the IMS recentered, and the new flange installed. I've turned the engine by hand a few times to check timing and it appears OK.
NOTES:
1) The importance of TDC is underplayed in the 101 book. Absolutely lock your engine at TDC. There's a reason those tools are in the tool kit for this job.
2) By "ok" my cam timing appears to be off just slightly on each side, on the order of 2-3 degrees. I have a plan to correct this.
3) I am an experienced mechanic and should have known better about note 1. But hey, the book said!
4) It looks like plenty of guys and gals got bit by this before me, reading through their trouble helped me fix mine. So thanks to all the others that have posted about this...telling the entire internet that you might have possibly f@$ked your engine isn't easy.
5) Read note 1 again
If all works out well, I'll report back on what my "minor massaging" entailed in case another poor soul falls down this hole and needs some food for thought.