28/29 frames are drilled/punched for LHD and RHD . 30/31 frames are set up only for RHD in England . . In USA 30/31 are set up for LHD only. The variation seems to follow what front crossmenber is installed for low rad 28/29 or high rad 30/31 . Some English and also Canadian frames were not serial numbers stamped .
John in cool dark no rain Suffolk County England.