Going to the autorust website, it says all A-body products were discontinued in 2018 and to go to Classic for any sales. So, just FYI, I would 100% call Classic to confirm they're actually in stock before ordering. Because Classic has totally "sold" parts they don't have that have been discontinued before.
That actually doesn't look bad at all, I would just weld the tab back to the frame rail.
This was actually a TSB from Mopar back in the day, they advised welding a gusset in there on cars that had the issue. You can see the full size versions at hamtramck-historical, but here's the preview