as far as im concerned the only dimension you need ot worry about is how wide the seats are.... for example a longer seat (from the back of the seat to the end of the place where your butt rests, would only be a matter of comfort, someone witha small butt and short legs would like a shorter seat in that respect
same with how tall the seat is, it's whatever is comforatble for you, as long as its not sticking outa the roof.... racing seats are ment to be comfortable for the individual, thats why there are so many diff sizes and shapes, one for every body shape....
(i need a plus).... btw ill be in touch with you ina bit i am starting my 3800 swap