This is a drawing of the Solarbotics GM3 Gearmotor. These little motors are awesome and are used in a variety of projects. I use them to build extruders for my RepRap machine.
You'll want to use this drawing as a basis for your own work. Use the drawing for an idea of where the motor will fit, its size, and where the mounting holes.
If you're doing a lasercut design, you can put the motor where you want it, then cut out the mount holes and your motor will mount perfectly.
The drive shaft is also the proper size to be cut on a Epilog 35W laser and come out nice and snug.