There are multiple sources of brown in an emulsion: it could be brown stain (think pyro developers), it could be some form of fog, or it could be tiny silver crystals which carry important image information. A bleach will get rid of brown image in the latter two, but in the last case you don't really want to. Since DR5 suggested that Rodinal is no good for reversal development, I suggest everybody follow his advice and look at more suitable developers for B&W reversal. I don't think many here can match DR5's practical experience with b&w reversal ...