I added the Solidworks files, they are messy but if you want to make changes this may make it easier for you.
Update***
I have added a ver2 of the servo holder for the drive servos. It moves the servos close together to bring the tracks up on the base's posts better. It also has thicker arms and is a little taller, there was not much room to adjust the tracks before. I have tested it nd it works and also brings the idlers all the way onto the base.
Note***
If you build this with the kit and it comes with the bulky screw on battery disconnect it will not fit in this orientation. I cut the end off an old battery charger and soldered it to an on/off switch I mounted under the car. It will work without the switch of course but I forgot the kit comes with a bulkier plug. You can try turning the board box around so the plug is in the front if you want.
First thing I did was buy the EZ-robot Kit at http://www.ez-robot.com/
This kit has all the electronics I used for this project.
Print off some pieces...
106 tread pieces
2 drive gears
3 servo holders
4 of http://www.thingiverse.com/thing:71033
and 1 of all the other pieces.
The track is assembled by putting 53 pieces together in a loop using 17Ga wire nails. I used one inch nails and had to alternate the side I started in because some were shorter than others and would cause weird stretching if I did them all from one side. The holes are purposely tight so that the smaller side will hold the nail in place and the outside does the pivoting. The servo holder for the drive servos are slotted so they can be pushed up to tighten the track. This can be done with the drive gears on or off, there are slots that will allow a precision screwdriver through to tighten screws.
The pieces that mount to a servo, (camera, ultrasonic sensor, drive gears) are designed to have a servo horn attached and then mounted with screws to the appropriate piece. Some servo horns I had to drill out the hole to accommodate the screw.
For the Ultrasonic sensor there is a 4 pin connector that you need to attach wires to. Best thing I found was to dig into an old tower and cut off a usb header, then solder that to the wires for connecting to the EZ board. That way there isn't a solder t right where the ultrasonic moves back and forth.
The kit comes with a 6 AA battery pack that I have mounted underneath the base, and there are pre-made holes for everything that I have attached here.
I am not sure what everyone will need/want to know so any questions feel free to ask, I will try to update more when I get more time/ambition.