The plenum spacer kit is supplied with spacers and longer bolts to raise the height of your strut to accommodate for the height increase of spacer.
Also if the page says £159 it will be £159...never any hidden costs with Adrian
As Jeff said, they come with spacers and fit the OEM strut bar, not sure about the one you have, but if that's made not higher than the OEM one, there won't be a problem with the fitting. The price is also correct.
Adrian