A 6'2" tall woman is a useful reference for deducing headroom for other women (who are 6'2" tall), but little more. Men typically have longer torsos and shorter limbs than a woman of the same height. You can even see it in the picture where Jean a male at 5'10" has a visibly similar length...
Rod, to the best of my knowledge there is no cam-locking buckle that is DOT approved (now someone will pop up with an example to prove me wrong). It is my understanding that DOT requires all seatbelts to be button activated so that removal protocols are universal for rescue personnel.
Best way to obtain a baseline may be to chalk the tires and adjust pressure to optimize contact patch. But someone with a great deal of experience told me good rule of thumb was a pound of air pressure for every 100lbs or vehicle weight would get you in the ballpark. From there you can alter...