Need tips on radius cutting rear wheel wells

Air shocks and shackles my man, BAM!
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Just kidding, I vote for what abodyjoe said, unless the quarter & wheelhouse are rusted out already, then hack away. But if you think you are into cars long term, replacing quarters & outer wheelhouses is time better spent doing more enjoyable improvements, like just adding inner wheelhouse extensions & spring relocation kits.
I think even as badass as they were, the original 68 Hemi SS cars looked hacked back there.