Bob, as long as run a 12.0 or slower your fine, but with your engine combo we can forget about that. I'm actually in the same situation about the interior. I really hate the idea about the cage, but if you want to have fun and open the car up at the track you have to have one. Here's what I'm going to do: I want the interior of the car to be as close to stock as possible. So the stock seats, carpet, etc. will all be going back in. I purchased an 8-point roll cage from s&w that has the normal hoop, front & rear bars, & crossmember. I also ordered their pro-street kit which sends the rear bars up and over the back seat and through the package tray. As for the cross bar I ordered an extra swing out kit allowing me to attach it with s&w's removable pins. This way I can run a 5-point harness when I want, or take the bar completely out. As for the front door bar, you only need the driver's side to be legal, so you can set that up the same way with the pins and just leave it out of the car for normal driving.
1968 SS 350 coupe, w/ 406 inches of tremec shifted mouse.