As per the parts book the seats shouldn't be any different to a concurrent model with different engine. Because you have slide adjustment it limits any possible seat frame variation.
However the 'quality' of the reproductions seams dependant on whether the buyer is interested the right item or not. Plus that the deluxe trim was in use for ten years and they weren't all exactly the same, something not mentioned by any of the reproducers. More of a general styling for people that have no trim, totally knackered trim or pay little attention to detail.
As map says, nothing unique about Stage 1 seating. Some Stage Ones had front seats the same as other Series 3s, others had the kind that were continued on into the 90/110 - I have both, one style in each of my vehicles. Have you looked here? :-
Not a recommendation per se (I have bought seat bases and trim from them with mixed results), more a case of not knowing any other source for seats anything like the original - Exmoor grew out of the people who made the original Land Rover seating in house I believe.
Exmoor and all the others I've seen as reproductions, all fall short of the originals. In the end I managed to find some originals in reasonable condition, that makes me happier.