Off the top of my head, you would mount the throttle link on the same arm as the brake link, and face the slide to the back (provided there's clearance from the spur gear).
I've never used a slide carb in my GT, but I have seen someone do it.
make sure you turn the servo around. It will give you more room. I would not suggest it though. When you have to feather the throttle there is no in between like a rotary carb. You are either on or off with the slide carb.
I just peeked at my GT but its an old one with tub chassis. To start with you will have to turn the servo around so the arm is forward. The throttle link will be connected to the inside (tank side)of the servo arm and the brake will be connected to the outside (body side) of the servo arm. Turn the carb pull arm to about 10:00 on the carb. Rotate the carb so that the line of pull faces the front edge of the servo. You may have to put an L bend in the linkage so that it will pull straight w/o hitting the fuel tank. Connection to the carb is made with a ball socket, they come in the throttle linkage kit but you may need to pick up a piece of 2/56 threaded link rod, if the link in the kit isn't long enough. You will also have to figure out how to mount a return spring to the servo. Take a look at the Losi XXX-NT manual for more detail Pages 48-51. http://www.teamlosi.com/ProdInfo/Files/XXX-NT_AD2_Manual.pdf Its a large file so it may take a while if you have dial up.