Ok, rear derailleur crisis averted. Not too much of a fuss to swap the piece, and we are good to go! I picked up a Campagnolo bottom bracket to work with the Medici's Italian threading. Anyway, the Medici's BB shell threading is in good form! The bottom bracket threaded in easily on both sides, and I installed the crankset (though not after a full cleaning and polishing). The crankset is a Chorus 10-speed and it is in great shape. The headset was also repacked with grease. I'll need to tighten and adjust everything, but progress has been made there--no forgetting once it's all built up!
[And in a bit of an aside, the present state of available cranksets (and parts for that matter) is, as we know, unsettled. From Craigslist to Ebay to LBS, the general theme I see right now is that unless one is getting a deal for something below $50-60, that $50-60 range is the transition point between decidedly rough or rougher examples below, and nice examples above (usually, WAY above). So that range becomes a sort of 'floor' if you will, and well, when you find great cranksets on the floor and rough cranksets just beneath those 'floorboards', the problem solves itself. I don't have access to a shop to run my buffer to spend a three hours (hopefully) bringing back a $40-50 scratched-to-death Sugino Mighty (or gen 1 Dura-Ace, or Superbe, or 600 Arabesque etc) crankset in a too-short length. I can't find a decent Maxy or other Sugino that would work, so it's really not an issue of sticking my nose up at 'lesser' cranks. They just don't exist outside of 'beater bike' condition, and if they do, online sellers see fit to ask $60+ for them. Some things fall through the cracks. People had weeks to buy that Chorus crankset, but I guess that 175mm length was too much. Who knows. It's also winter and only the perennial bike enthusiasts are on the continual hunt. I would love to find a pristine 1987+ Shimano 105 groupset and just build a (tall) bike with it. Matching hubs, too, laced to decent rims. Vittoria Corsa tires etc. Find the frame for not much, build a bike for not much. But 105 is often the transition point in component condition where there are more 600 and Dura-Ace components available in good condition than there are 105 and below in good condition as the lower-ranked components are subject to harsher conditions by perhaps negligent owners over a longer period of time. I still want to build a bike with current gen Claris (R2000) or Sora (R3000). Great looks, proven components, fantastic STI shifter shape and feel, and great price. Just need a frame that goes with it.....]