Kent,
What are you looking for in a seat? Are you tracking the car or are you strictly for the street. If you are thinking of tracking the car you may want a five/six point harness. That will require a different type of seat. If that is your goal, I would suggest the ones I am using. Racetech. If not them, you will need a seat that has the cutouts for the belts and is semi reclined to fit against the firewall. They will hold you in the seat without sliding around. I rode in several GT 40 before building mine. They weremore period correct seats and very comfortable while riding along in them, but rounding corners at speed I felt I had to hang on to something like the dash or the door. If a three point is your choice, then you have a wider selection.
One last thing to think about is, how big is your butt. If you are a "big boned" person, then the choices become limited. Racetech has a built in graphic that gives you the measurements of each section of the seat. I am 5-9 and 160 and over sixty(different body proportions), and I fit very nicely in mine.
Bill