First of all. I like the idea of people trying to develop their own car
But why a car with shaft drive, most manufacturers switched to belt driven cars, because it makes the handling better.
Best one of your pictures, but how about turning the servo 90 degrees, with the receiver on the outside end, and between the battery and the servo/receiver the speedo. This way you can keep the weight as much to the centerline as possible. and making the car pretty narrow. Downside, especially when using lipo is that there is a lot of weight in the front of the car, making the car understeered.
You want to have the receiver underneath the shaft?? This means both the shaft and the diffs for it should be in a high position, and higher your weight means a high center of gravity, which doesn't improve the handling of the car. Also this car would be very under steered, because there is too much weight on the front half of the car. Always try to keep the ratio 45% of the weight in the front, 55% of the weight in the rear. Also the servo in front of the diff will be bad for handling, always keep the weight behind the front wheels and in front of the rear wheels for good handling. Not to mention it would be really difficult with the wiring of the car (the servo wires have to go across the front diff, long motor wires as you mentioned yourself)
Somewhat similair to the Losi (except for the servo), but like picture 2, there is a lot of weight in the front, especially when racing Lipo. Also here the wiring would become really difficult, because the receiver and servo are on the other side. And just like in picture 2, the servo all out in front of the diff will have a bad influence on the handling.
For a good weight balance try to get something close to this:
LR: 27,5% LF:22,5%
RR: 27,5% RF:22,5%
Also I think a belt driven car would work out better.
But most important, when you have doing it, keep on going. And keep us informed on your updates.