This upgrade kit replaces the shoulders of Combiner Wars Firefly or Sling with parts resembling Harrier jump-jet nozzles. This will make your custom Slingshot figure more G1-isk!
The shoulder pieces are straight-swap. The rear nozzles need to be glued on to the lower arms, and to do that you must cut off the middle-finger guns.
More information on the TFW thread: http://www.tfw2005.com/boards/radicons-customs/1033020-shapeways-combiner-wars-fireflight-slingshot-upgrade-act-2-a.html
Also check out my Fireflight wing upgrades!