I guess I would ask, crunch-wise, what would the system require to run a DL game?What crunchy bits exist in DL that AD&D may have that clones may not?
From what I recall of the original book trilogy (I avoided the modules like the plague after I read the first way back when), everything could be modeled with AD&D, 2E or the most of the various retroclones as written- even S&W WhiteBox can do it with some minor crunch/fluff design for paladins, and the varying races (kender, gnomes).
I'd say pick whatever you like to run for PBP type games and do a little bit of crunch writeup if need be.