My younger brother is about 5'9" and over 500lbs and is driving around in a 1966 VW bug. I don't see how, but he does. I did add a 2" block to the clutch pedal to space it closer so he can sit sideways.

Those fox bodies have week floors. I broke the floor in mine and I was 180lbs. I wonder how much is contributed to driving hard. When you buy some frame connectors for these cars, they have reinforcements for the seats attached.