Cowl Rust Repair Options

[Jim70Chevy]

As I am tearing down my front end to clean things up and repair rust I am finding the common rust issues inside the cowl (and leaking in the cab).

I have done a bunch of reading of threads and builds here but not been able to find the answer to the following question.

Can I cut a hole in the outer panel (as shown by red line in picture) to fix the rust and make my repairs then weld the panel back into place?

I am trying to avoid having to replace the whole cowl piece but that may be the only answer.

Thank you in advance for your thoughts.

Jim