Cowl vent replacement surgery

[Oldboy]

Hello,
Wondering if some would give feed back on this repair i wish to make.
Little back story: 46 plymouth business coupe, cowl vent, while it works mechanically, is rotted out completely in the troughing channel , which collects water, and sends it out via a collection tube.
I was able to cut out a complete cowl vent mechanism from a donor car, pristine condition.
I actually cut the area from the cowl on the donor car oversize, taking more than i would need.
My question is this, do i need to brace my car in anyway before cutting out the rotted section? Can i just make my marks in sharpie and cut away?
Plan on mig welding the new section.
Thanks, Russ

 

[Blue Eyed Devil]

As long as you aren't cutting into the windshield opening you should be fine. Step away from the sharpie though. You will have a much nicer fit if you mark with a scribe. Makes things a lot easier and faster. The finished product will thank you for it...

 

[Oldboy]

Cool,
Very nice. Thanks for the speedy reply. I am anxious to start this repair.