Twin C5 Lockheed Galaxy

for a while NASA was seriously considering building this for the shuttles so they wouldn't have to use commercial airliners. It was also theorized that they would have used it as a test bed for Air-launch-to-orbit systems. Meanwhile, Lockheed just designed it so they could increase carrying capacity without having to go back to the drawing board.

Based off of Peda's model
https://www.thingiverse.com/thing:364446