[Citroënbender]

Tough one, you’ll need to be careful of not overworking the sheetmetal. It looks like your worst creasing is above the larger part of the bracework, too. Also remove that underfelt before starting, you ideally would use a trim clip tool.

I’d look at removing the airbox only while actually working, you can possibly brace underneath down to the chassis rail. A bit of 2x4 pine with marginal doming to the head for that brace, will be good.

If you had two good arms/hands you might look at starting the job with it face down on a mattress but solo bonnet R&R is not much fun, even so.

There’s a bloke advertising an engine-less AU in Duncraig, it’s on Dumbtree for $350. See if he’ll swap bonnets with you for $120-$150 if it’s correct and mostly undamaged.