My group has run through all of the official adventure cliff plunges for DCC (including 3rd party)
Does anyone have any suggestions for published modules that can be converted that are in the spirit of DCC?
Barrowmaze is good -- but I've found that the true "dungeon crawl" in the ilk of Basic/AD&D is NOT in the spirit. Yes it's called DCC, but the idea is the short, painful hellish adventure that continually defines the characters that survive. The dungeon crawl/megadungeon is an endless slog through monsters and traps that everyone has seen before. And of course, those old adventures (and Barrowmaze) hand out treasure like candy on Halloween.
I'm taking Barrowmaze and cutting it up into distinct, but related adventures. His undead additions are great and the idea of Barrowmaze is fantastic -- especially the tripartite fight between Orcus, Set and Nergal. For DCC it just needs less crawl and more Appendix N.
Actually -- the adventures by Richard Pett (of the "Styes" fame and others) in Dungeon magazine are well within the DCC ideal. These are 3.5 adventures, but they are essentially Call of Cthulhu filtered through D&D.
For that matter, pieces and parts of Call of Cthulhu adventures would work great for DCC. You'd have to gauge how much your characters care about research/roleplaying, but the adventures can be toggled accordingly.