Just thought I'd pop in and add a little update to this. I have loose involvement in this with it being a friend's car belonging to Tommy.
After a seized front alternator bearing, subsequent bursting of a heater pipe put it out of action for a while and 3 MOT passes later, rust has finally caught up with it.
Nearside front floor / jacking point / inner sill:
Offside front floor / jacking point / inner sill:
Going to have a think about it, but will probably fire the welder up.