[KensRedZed]

I humbly apologize. I have never made a 4WD chassis before.

To make an aluminum chassis, I start out with aluminum square tubing (3/4" x 3/4" x 1/16th wall). You'll need a small drill press, and small bandsaw to make one.

Here's an example of a front motor drive chassis with a drive shaft.

   

To make a 4WD. You'll need to start with an S-can motor with drive shafts coming out of both sides. Install the motor for a direct drive to either the front or back. Then use a drive shaft to the other side.

   

You'll need do some changes to make it a 3-post body mount system. Body posts will need to straddle one side of the motor shaft. It can be done.

Please let me know if you want more details.
Ken