Have made some more progress, have the bottom patches welded in, working on the top ones. I decided to ignore the welded seam on the boot floor and just do the one panel, I ummed and ahhed about it but realised when all's said and done it's going to be buried under seam sealer so there's not much point making it look more aesthetically original.
You can see in the below photo there are some extra welds from what I assume is a historical collision repair. The inside of the back panel definitely looks like it's been beaten back into shape. Otherwise, behold: my mediocre welds!
Test fitting upper patches: