Repairing a rusty cowl on my 72.

[BigBird05]

I've got a question for all of you body men out there. I have a rusty inner cowl. I know strange, right. You can see day light thru it above the brake pedal. I was lucky enough to find a rust free inner cowl at the junk yard, so I bought the whole upper half of the fire wall and dash. My question is should I only replace the bad rusted out piece and have a seam that runs about 30 inches long and leave the windshield frame alone, or replace the whole inner cowl for about 30 inches, plug weld the fire wall and windshield frame at the spot welds and only have about a 8 to 10 inch seam over by the wiper arm mount.