Guys, guys - I'm not arguing any of the things suggested but I am (at least nominally) at work - a quick jaunt out to the garage to check things is about as much time as I can spare at the moment. I've noted all the suggestions and will try them in good turn.
I did just pull the disto cap. It's running one blue and one light silver spring, as I guessed. I can't tell the color of the stop but as it goes from 15* initial to ~38* total I'd guess it's a 21* stop.
The interior of the distributor shows a lot of corrosion - the prior owner lived right on salt water and it shows throughout the car in minor bare-metal corrosion I'd planned to take care of over the winter. He told me he'd just replaced everything from the rotor to the plugs because of corrosion, but he should have started with the distributor itself. I think it's completely functional, but it's not good and certainly not helping anything to have that crud in there. (Honest, it looks like something off a poorly maintained boat!)
So that MSD kit will likely come with a complete distributor. Oh, joy.