Two quick checks. Straight gear shift lever=WD, curved=WD-45 or very late WD. Look for a bolted on side plate on the right side of the block. Side plate =WD motor, no plate,=45 motor. Beyond that check the area above the rockshaft and below the brake cover on the left side for the serial number and check it against the serial number reference to the left of this page. Here is a link to a page that shows the location.