I love this build, it looks very well thought out. But, I have a question about your swing arm: Are you going to add additional material between the two sides of the swing arm to prevent it from twisting around the cars roll axis (one arm going up, the other arm going down)? Even motorcycles join the two sides of the arm and they don't see that much side loading from the bottom of the wheel (only from bumps while leaned over turning). For example see this picture of a Suzuki GSXR-750 Swing arm:
For more interesting examples of motorcycle swing arms I found
this page. They all have lots of additional material to prevent twisting.
You shouldn't count on the ends of the axle to provide the kind of stiffness you will need.
[edit] I have some time now so here is an idea of the loads that swing arm may see:
Assume you finished car weighs 1500lbs in road going trim, with driver. 50/50 weight distribution, and going through a 1G turn. These weights might be high, but the cornering estimate is probably low for modern sticky rubber.
The O.D. of you rear tire is probably close to 24", or 1 ft radius. Around said 1G corner the rear tire will have to provide 750 lbs of lateral force for its share. That lateral force acts at the tire patch, 1ft away from the axle, which is where the side loads get transmitted to the swing arm, and from there to the rest of the car. So your swing arm is going to be twisted with 750ft-lbs of torque. Without any additional torsional stiffness in your swing arm all of that torque will be opposed by the ends of the axle that are bolted through your swing arm. 750ft-lbs is a LOT of torque. You could probably do some serious damage to your swing arm in its current configuration.
Now this line of thinking ignores the dual shocks you are using, which should reduce this effect over what a monoshock sportbike swing arm would see, but it still bears thinking about.
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