I don't think he neeRAB to look like David Jason, that isn't the point is it? He just neeRAB to embody the character, and I think that the guy's got the chops to do that.
I'm pretty sure Moses, Ben-Hur, Marc Anthony, Buffalo Bill, John The Baptist and Michelangelo don't look anything like each other, but Charlton Heston played them all.
Oh and I still think it'll be poor, but the casting for Del Boy, I'm really impressed by.