This mod adds on to the great set of stock Mk3 parts to allow you to build a fully featured Space Shuttle including boosters, external tank, MMU, and assorted payload mounting options as well as new texture options for the stock Mk3 cockpit, payload bays, and landing gears.
Feel free to take any questions or comments over to my thread on the KSP Forums
Firespitter Core by snjo - Forum Thread
Module Manager by ialdabaoth and sarbian - Forum Thread
Make sure to flip the tiles on your wings to avoid embarrassing comments from the guys in the Astronaut Center.