Yes, Lollobeeb, it is in DADGAD - Capo at 3rd fret as you have worked out.
I've been a fan of Boo's songs for years, he's played twice at a gig I organised, and stayed at our house. He showed me how to play a few of his songs, including 'Bell, book & candle' but I still haven't mastered it.
He's playing open strings with a simple melody following the vocal.
What I can't master with his own version of this great song is he plays a double beat finger pattern on the bottom string which I just can't get.
There's a guy on Youtube who seems to have got a simpler version sorted, which is nearer to Eddie Readers version.
Search for 'Bell book and Candle (Boo Hewerdine cover)' and the guy is Laurence Eddy. The video is pretty clear so you should be able to see what he's doing.