For the 5 stud wheels it's 5 x 5" or 5 x 127mm. The front hubs for the Plus 8 came from the Rover P5 3500 saloon (sedan) and were, I believe, common to the Rover P6. As regards the Rover SD1 hubs beware as the stud size was converted to metric and was oversized slightly.
Unfortunately my knowledge of the PCD for 4 stud wheels fitted to Morgans is unknown to me.
