The massive steel sub-frame seems standard on FF/CMC since their start using the original IM tooling. Believe some kits were sold with the sub-frame not installed (rivetted and bonded) to the fiberglass body. The early build manual shows attaching the separate sub frame to the VW pan and then adding the body to it. You can buy just the fiberglass (and just the sub-frame) from Kit-Man or Rusty Tubs (if they still exist?). Without the sub-frame, I'd think you'd get twisting and cracking of the fiberglass body. I guess for a race/drag car it would be fine. I would think you'd need a jig to produce the sub-frame. I know of no measurements for the sub-frame. I guess you could do it.
I have a dune buggy with no sub-frame (most don't have one) - it has no doors to hang or even open nor much body overhang at either end.
