She's back from the dead! Blew out a huge amount of smoke upon starting (scared the neighbors off their stoop), then idled rough for a little. Shut her off, started her back up and no smoke on the second round. Still not as smooth as before, but I've only let her idle for a couple of minutes.

Good to know that it was such a simple problem. I think I'll continue to go ahead with the replacement of the spin-on filter, diesel purge and certain leaking fuel return lines, just for the peace of mind.