If you have a NFL Blitz / NBA Showtime Vegas system, you should note that it uses a Voodoo video card. The Gauntlet Vegas system uses an Obsidian video card, which means that you cannot run the NBA Showtime on a Gauntlet system without changing out the video card to the Voodoo card, and vise versa for the Gauntlet on the NBA Showtime system.
Now you can change a Gauntlet over to the Showtime by changing out the video card as noted above, however the switch inputs for the joysticks are very different because the NBA Showtime uses the I40 PCB to interface to the 49 way joysticks and the Gauntlet does not use an interface. As a result, the controls will not plug and play. However, there is an easy way to make the sticks work by changing them out to 8 way sticks and bypass the I40 interface. Mind you, this will require a lot of wiring and time and should not be attempted unless you are very experienced with reading a wiring diagram and know how to wire correctly.