Hi dtunget,
I was about 275lbs when I bought my car. I'm losing some of that now for extra comfort both in the car and out. I'm only 5'11", so I know that you should have plenty of room width wise. As for height, my neighbor tried out my car and fit fine and he's 6'5. The key differences are going to be the ratio of leg length to body length.
My father is 6'3" but when he and sit side by side, I'm much taller. I've got abnormally short legs for my body height. That made it a little easier to mount my seat in such a way as to give me more head room. I just mounted the back of the seat tight to the back wall, and scootched the front of the seat forward to give the seat a little more lean.
When my tall neighbor sat in the car, his legs were a little cramped, though functional. He enough clearance though that could have sat the seat a little more vertically to give him some more leg room. I was worried that being more upright his arms and hands would be a bit uncomfortably high, but he actually found it more comfortable. He normally slouches over the steering wheel while driving his suburban, so he'll be in for a shock when gets a car to realize that there is no slouching with the harness on!
I'd say give it a try. You may be very surprised. It'll be a snug fit, but it won't be restrictive. You need very little room for turning the wheel, and if you change the steering shaft position, you should be able to make enough room for your legs when braking and shifting. The big thing will be to get a test in a car with a wide enough seat.
Good luck,
Mike
