First I put in the heelboard end. Having ordered the wrong part, this is actually a modified van section. It works well! Ordering the right part for the other side...

Then I started on the rear lip. Here's the new lip, joggled, with the old lip marked for cutting:

After some fettling and alignment, I spot-welded the new lip on. Not much room to wield the heavy spot-welder, so it was quite exhausting to hold the thing in the right position at different heights.

With most of the rear end done, it was time to cut away the remaining front sill & step in prep for the new step & floor.
Trouble is, the inner wing and sill has been patched - on both sides! Another rust sandwich, and far too many layers.

Pulled away part of the inner patch...

And the outer patch... so many layers, it's difficult to tell which bits are the original metal.

Finally got down to this... not a lot! It's going to need cutting away completely - at least that makes it easier to get the floor panel in.