uiBindingRegistry.registerMouseDownBinding(
	new MouseEventMatcher(SWT.NONE, GridRegion.ROW_HEADER, MouseEventMatcher.RIGHT_BUTTON),

	new IMouseAction() {

		ViewportSelectRowAction selectRowAction = new ViewportSelectRowAction(false, false);
					
		@Override
		public void run(NatTable natTable, MouseEvent event) {

			SelectionLayer selectionLayer = ((BodyLayerStack)((GridLayer)natTable.getLayer()).getBodyLayer()).getSelectionLayer();
			int rowPosition = natTable.getRowPositionByY(event.y);

			if(!selectionLayer.isRowPositionSelected(rowPosition)) {
				selectRowAction.run(natTable, event);
			}					-
		}
	});

selectionLayer.getRowPositionByY(event.y)

int rowPosition = natTable.getRowPositionByY(event.y);

int rowPosition = LayerUtil.convertRowPosition(natTable, natTable.getRowPositionByY(event.y), selectionLayer);