If your original cowl is rotted and you decide to replace the entire cowl assembly, here's a tip to help save you some pain later.

Before installation, fire up the mig welder and give some attention to the threaded studs that the driver and passenger side fresh air vent bolts to.  Tack weld around the base of each stud.
It seems the studs are barely spot welded to the lower cowl and when you tighten the vent nuts, the studs twist off.......Ask me how I know......taint no fun laying on your back, trying to weld those buggers back in place........

A JKB public service announcement.......