The first thing I fixed on my new Comet was a massive exhaust leak. I could not see the leak but I HEARD it and could feel the hot blast of air coming out from under the exhaust manifold.
First get the linkage and vacuum line removed, put away and set aside.
Get the flange nuts off too.. .be careful not to destroy the gasket.
The good thing about the straight 6 170 exhaust manifold is that it’s a perfect match with the straight 6 200 exhaust manifold you have on that old Mustang engine behind the barn.
Once you have the bolts and exhaust flange nuts off I recommend soaking them an afternoon in liquid wrench first). Line up the mustang manifold. and start the bolts a thread or two so you can line up the exhaust flange gasket and flange. You may have to just take the old one down to the parts place and get one by size if your exhaust has ever been messed with. Line the new gasket into place between the manifold and head after cleaning off the old gasket gunk. Once you can tell if the exhaust flange will line up and seal, tighten up those manifold bolts.
Tightened everything up, added the vacuum and throttle linkages back up and it sounded GREAT! It purred fine!
Here’s the cracked manifold! The new one is a huge improvement! Only took about an hour.