OK, I spent some time looking at this over the weekend - those of you that have enjoyed the entertainment value of this thread will be happy to know that I only eliminated some possible causes, but only just maybe now have found the cause.
First, for the doubters - yes, there is an engine it! OK, it's missing the airbox, exhaust, driveshaft, and battery, but that's not going to make 3"+ difference in ride height! You are all just hating on my because I picked up this abandoned beauty for such a great deal
I measured from the ground to the rocker just in front of the jack point - 10.5", so about 3" high compared to others.
I loosened up the nuts on the radius rod and the control arm, then did my best Greg Louganis impersonation bouncing up and down on the end of the bumper, but while the car moved up and down (it's not frozen in place), the static resting height didn't change. (OK, I stole this picture, it's not from my car - but these are the locations I loosened)
The numbers on the strut tube reference back to tii struts.
I did note that the strut top looks to be assembled with the spacer below, so I could drop them a little bit by reassembling the strut tops, but we're not talking about a huge difference - and having the strut assembled as it came from the factory obviously isn't the cause of this problem.
I then measured the height of the spring unloaded and under under load - 9.5" unloaded, about 2" less under load.
I could see that the both ends of the springs are seated correctly (and that the spring has white paint marks - I can't tell the underlying color). It wasn't until posting this just now that I went out to look up the color codes, I see "White 750-776 lbs" listed for rear springs - so it's looking like maybe the front and rear springs were switched? I've misplaced my calipers, I may have to go to Harbor Freight and pick up a cheap set so that my good ones will appear (because that's how it works when you misplace a tool - go buy a replacement and the lost tool immediately comes out of hiding) and I'll be able to measure the wire thickness.
Here's to hoping that the paint codes on the rears match up to what should be on the front - I'd hate to think that somewhere along the way springs were lost and they kludged together whatever they could. Even better, this could explain why I can't get any clearance for the steering idler link!