@Captain Obvious you definitely lived up to your name, the distributor was filthy on the inside. I was able to clean it up pretty well, and now it snaps back as expected:
There are two pieces of bad news though:
1) One of the springs is completely missing. Nobody seems to have these in stock anywhere. I suppose I could run with just one spring for a while, but it's not ideal.
2) The breaker plate assembly is pretty locked up. I didn't try pulling it apart, but I give it a 50/50 chance I lose those little bearing balls when I do. I can also buy a "new" one for $50.
So, my question to you veterans is what's your advice? My immediate goal is to get the car up and running and drivable so I can have a little fun before I start dumping too much (more!) money into it. Longer term I've been following @jonbill's speeduino progress which looks like a ton of fun, so I'm not too excited about dumping $600 on any of the fancy new distributors (123, Kameari, etc). Is it worth retrofitting a cardone 280zx unit, or am I better off getting that new breaker plate and running with 1 spring? I've heard good things about Advanced Distributors rebuilds but I'm betting they're spendy and the lead time is 6-9 weeks which is a bummer.