That issue became a non-issue once NHRA placed it in the rule book as "factory type". That's about as vague as you can get. The seats in my AMX when raced in Stock were from a "Renault Le Car Ralley" as Renault once was a partner with AMC.
Now that this AMX is a Super Stocker, I have the same seats and they look very similar to a Porche 911
And I have never sat in a drag race car with a better fitting seat. Found them in a wrecking yard front office for $100 each and the upholstry was great!
Food for thought; I've always thought what looked best was the period correct look. In other words, a '70 Challenger high back just doesnt look right in a '68 GTS and the opposite is true. If your building a '70+ mopar, a cheap very light high back seat is an Omni or other K car. Also take a look at a VW Rabbit or similar. You can pull springs and hardware out of some of these import seats and have a 15#-18# seat with solid mounting (which is legal).