It may really help this chin if you give him a "human" bath, using diluted baby shampoo. Work quick, rinse quick and be careful not to get any water in eyes, ear, and mouth. Pat dry with a towel and then blow dry on a low setting. Comb out when dry and then have him do some nice big dust baths over the next week or so. You should see some improvement after a couple of dust baths, and I'd bet he'd feel a ton better(at least when he forgets about being shampooed). When he puts on some weight, his proportions should improve.
I have one chin, with continuing dental probs, that drools on his cagemate's back(Cliff calls it Droolback Mountain)pretty bad, so I have to occasionally give his back a wash. It's not a big deal. There are times when chin dust just can't do the whole trick - doesn't happen too often, thankfully.
Hope this guy's happy with his new family. Can you send some type of supplement with him when he goes? He could use a boost.