Thanks, everyone for the advice. The news is... it still seems to run!
Turned 'er over on the starter for just a second to make sure nothing was frozen, dumped in three quarts of oil (drip pan underneath to prevent another "Exxon Valdes" moment), then pre-glowed and let 'er rip. Started, pressure came up, and it ran just like before! (Although the power steering pump sounds suspicious, probably due to factors other than the Valdes incident.)
Now that the roadway's dry and I can read the telltale tracks, it appears it was driven just once on a short errand after pan met pavement. Abundance of oil under the last parking spot says there could have been oil remaining right up until it was parked. (Whew!) Too bad about that four quarts of oil spread on the environment between here and the store...
Much as I'd like to read my testimony on the back of the J-B Weld package (thanks, WmHarlow), I think this is a pull-and-replace job. The normal rounded edge of the pan is creased, sharp edges apparent from partial tear-throughs, and some of the drain plug is involved. Looking at it, I can have that baby off of there in 15 minutes, and parts are less than $30.
'76 240D @120k