Take one grill panel. It doesn't look too bad really, does it. Until you spot that someone has welded a bit of bar over the rotten mess at the bottom.
Remove said bit of bar, and it seems that there isn't much to the bottom of the grill.
There is even less left mind you, once I've attacked it with an angle grinder.
Now, cut and bend the repair section you got folded up earlier, until the top edge matches the bottom of the grill. This bit gets time consuming.... eventually, it should fit. Thin cut "plasma" grinder disks come in handy here.
Then its just a case of lots of welding and grinding flat. Lots. That and sorting out the little backets the gril hangs on at the bottom, which I haven't yet. I should get it finished off tomorrow, if I muster the enthusisasm.