the difference between FF and RR coilpacks.... as far as i can tell, it's the orientation of a small vent/drain hole on the rubber seal just under the main body of the coilpack.....
the rear is on the same side as the connector socket...
https://farm5.staticflickr.com/4318/...b434a94a_c.jpgWP_20160507_12_12_33_Pro by jon sutherland, on Flickr
the front is on the opposite side...
https://farm5.staticflickr.com/4312/...5db7659a_c.jpgWP_20160507_12_12_51_Pro by jon sutherland, on Flickr
the rubber can turn, so if you needed a rear and only had a spare front..... just saying :)