I managed to get a hold of Wells's "Accents of English" and he mentions that 'Boston short o' that I was talking about a few weeks ago. Apparently it was already rare in the '30s, so I wouldn't be surprised if it were extinct by now. It seems that some words in the GOAT set had [8] instead of [7U], so that 'road' [r\8d] was distinguished from 'rode' [r\7Ud]. Wells says that East Anglia has (had?) a similar feature, so that could be where it came from. I have to say, I've never heard this pronunciation, and [8] in 'road' sounds very strange to me. Just thought you might want to know. :-)
Boston short o again
Oh, okay. I've never heard that pronunciation, even in elderly speakers with really conservative accents, so I think it's probably extinct now. (I have read about that distinction being preserved in East Anglia, though.)