Report Early Avanti front seat reinforcement in 1963-64 Avanti Posted Sunday at 10:44 PM In order to do a conversion, you would need to fabricate the steel frame for both the seat bottoms and top. The horseshoe shaped filler panels are made out of a material similar to Styrofoam. You could likely achieve the same result with upholstery foam. As far as upholstery goes, the seat backs are 3 piece instead of the single piece. When I get home in couple of weeks, I will post pictures of the later seat back upholstery.