I don't understand how drive shaft length would be any part what so ever of the "planning stages".
You set up your car with the look you want, THEN you simply make the drive shaft that fits where you have put the components!
Spend the time setting up where you want it to get the look you are after. Stand back and look at it, move the rear end back and forth in your mock up to see how that changes the overall appearance.
DO NOT do this without the wheels and tires you plan on using. Moving the rear or front axle a half an inch forward or back can make a HUGE difference on the appearance of the car.
Spend your time setting it up then simply measure off where the drive shaft goes and get one made or make it yourself.