Hello all...newbe here. I have a 1970 351C 4v Mach 1. Love it! I am considering taking off the headers and replacing them with stock exhaust manifolds. Headers have leak and look nastie. I know I will loose power.....someone talk me out of it!
Great site for mach 1 lovers!
Welcome.
Well, if you have all ready purchased the manifolds and trying to finding those and then paying for them didn't kill your thoughts of making the switch - I would say that you are pretty well decided to make the switch.
I don't know that I would try to talk someone into or out of either headers or manifolds. Back in the day, it had to be headers. Nowadays, well I must be more mellow.
Ha...Finding them wasn't too hard. Craigslist and Ebay both have some listed. I bought a pair of 1971 exhaust manifolds and was told they would fit. After purchase, I realized the drivers side for 70 and 71 have different exhaust exit angles. Not knowing for sure if that would create interference w steering box or FMX trans etc., , I bought a correct pair of 1970 manifolds. Now to install them....not looking fwd to that!
Well, now you know. 
Anyone need a set of 71 351C 4V exhaust manifolds? 
I would recommend cleaning them and using some Eastwood type high temperature exhaust cast metal paint on them before installing them.
Just be thankful you have a 351C and not a 390 or 428 FE when it come to exhaust manifold removal and replacement!
Welcome to the site. Please, Please do not put the stock manifolds on...think about the horsepower you're going to lose and all the weight you will be adding. Plus it is a rule that if you install the stock manifolds and go to car shows you must keep your hood closed at all times!!
Okay, I tried to talk you out of it. Kidding aside, there is nothing wrong with going back to stock manifolds other than making everything fit and line up again. Please keep us posted and share a picture of your car.
LOL...Glad someone opposes the stock manifolds! It runs good and sounds like a beast right now. Air Conditioning is next for her.