You need to put spacers between the metal backing plate, and the suspension arms, in the area that goes around the bigger ball studs on the center chassis section...
Then, depending on luck, some slight trimming on the suspension arm on the endbell side of the motor...
A lot of people also just run the 17T Speedgem motors... But with mod motors, unless specifically designed for the truck, you will have to take the motor apart and turn the endbell 180 degrees on the rear motor.