Where as the plastic seats find strength and less mass with their molded composition, the A100 seats which by chance were also used on the Hurst Hemi Darts and Cuda's found their light weightlessness in a very spartan frame work underneath. Rather cheap for those low grade work vans they were standard on.
The foam and fabric were miniscule at best. A-100's, Their only draw backs is no upper/neck/head support.
Ford Thunderbolts, Merc Comets, Battlestar Galaxies and I believe a few Chevy 11's had a version of them also.

By the way, the original split front bench seat with hardware was 100 Lbs total. Probably a little less for the ones on A-cars.