Rattiac, i believe your on the right track.
If you make a posterboard template first, (follow the slight convex curve that the cowl makes), then mark that a 1/4" back for your lip to the body side. If you follow that line and slowly bend with vise grips, then smooth out by tapping with hammer on a vise... that will still have the curve. I'd leave an 1/8" gap at the body and get some 3M strip calk (or similar) to fill the gap on the lip. Strip calk won't harden and can be removed.
Then cut where needed on the toe board. I would use the wide head trim screws to fasten to the floor so you can easily remove if you need down there.
Just a thought😁