The seat buckets are very much like those used in TVR Vixen 2500s (and likely other models). The buckets are just a fiberglass shell.
I will update this thread very shortly with a picture. The yellow insert could be custom made. It would just lay down the center of the seat bucket.
I wonder if somebody like Summit or Jegs have a generic aluminum bucket that these type seats could be created from?
I’ll post up over on the TVR board, and see if I can find more information about the availability of the buckets.