I'll stick my neck out here and say (about those boxes running along your rockers/ sills): "definitely" *non*-original, unless somebody knows differently...
either a not-so-DPO addition, or some Rally / Rootes Competition Department stiffening ??
p.s. Gary (et. al.)
>"Then the "L" shaped inner was hand formed" (I also found that the bottom
>section
>needed to get narrower at the rear)
sounds like some serious metal-bashing, in 2mm mild steel ! You can buy either complete central sill or it's lower half from most of the uk suppliers. there are some tricky curves at the front & back edges.
A