Neither of the bikes above have disc brakes- is it easy/possible to convert to disc
Emphatic No.. if you want a disc brake nice touring bike, buy one set up with them in the first place.
may not be able to do it on the cheap, and used, unless someone hated it .
Or got it for a trip, finished the trip and is reselling it..
Surly LHT Disc, people like theirs ,
just get the money together, and buy one, new, from a bike shop.