Help with Cowl side panel

[Taylorxmk]

Has anyone here tackled replacing the side panels on these cars? my passenger side looks like swiss cheese and I have a repo part in the garage but it appears to be sandwiched between the rocker and firewall. am I mistaken? I'm assuming it will be best to tackle this part while i replace the full cowl

 

[YellowHorse]

Could you even locate to buy this part?