Cowl vents where to get these?

I ASSUME THAT you mean the metal "top hat" in the cowl itself not the plastic air box that directs air to the floor?( if you need th interior vent assembly hit the junk yards three bolt job) If noto there are repro parts for the mustang out there that weld in. and plastic "hats" only that glue in from the bottom. If you want a more permanent fix, hold on. First remove the upper cowl (peice where the wiper shafts are). This may be bolted in or welded ( idon't remember the year of the switch over.) if it is welded the windsheild must come out and you then remove all (about 90) spot welds around the cowl frame. With the cowl lifted off you will see the under cowl, this is usually what rusts out and leaks. Start making patches, throughly prime and paint when finished, check to make sure that the drain troughs are open and that no water will lay on the cowl. reinstall and spot weld cowl inplace, prime all weld marks and touch up paint. reinstall windhseild. Local shop here in west florida charge around 1500 bucks for this job.

Thanks for you instructions, The plastic hat where do I get this part? Thanks Dave.