Car with a roll bar and back seat look cool, but the practicality of it, is not high. To get into the back seat they will have to climb over the crossbar, not to mention you have the 2 down bars. If you run the down barns closer to the door panel/outside of the interior, you might be able to have someone sit in the middle of the rear seat. I'd still be concerned with them bouncing their head off the down bars at some point during a ride or crash. I have 3 "muscle cars" 1 is my street car, and the other 2 are race cars. The race cars have a roll bar and a roll cage. Either build a true street car with no roll bar/cage or build a street/strip car with a rollbar, but don't plan on using the back seat for actual passengers.