Option 3, no go as the crinkle high spots are pretty high unfortunately or I'd do that!
Option 4, cut the inner support rail out and can access the area better.
Might even change my welder to run 'dry weld' Deano style gasless for the time being..
Now that the majority of welding is done finally, there's just some touch-up places to rectify.
1, rear seat base supports
2, fuel filler new hole in C pillar
3, new modern exhaust hangers
4, adjust radiator notch to fit ally radiator, whether it's the Escort one or Gemini one, I'll redesign the mounting arrangement either way.

I have a oxy set but no bottles and the amount of times I'll use it isn't cost effective.

Option 6, use Tig as oxy on a low setting and ball the electrode so the plasma goes in a wider area , give that a try !