I think Simon,in addition to the Martin OM he plays,has for a long time used a custom Yamaha;jumbo-sized,black with rectangular pickguards on both sides of the soundhole.......in Canada,Murray McLaughlin and Sylvia Tyson also play them,theirs have white pickguards.......only three I've ever seen;I've heard McLaughlin's and it's very impressive.......I think they were only a special-order item some years ago..........