I bought a 77 F-150 4x4 a few weeks back and have been working on getting it back to emissions standards for Colorado. I took it in today and it failed due to not having an air injector pump. The drivers door is not original so there is no warranty tag with a DSO code so they said they had to assume it was supposed to have an air injection system.

Most of the 351M engines I have seen have the air pumped into the back of the heads via bent tube. There are two types, one where the bolt has the air holes in it and the air flows directly though the bolt, the other one bolts to the back of the head and the air holes are offset from the bolt holes. I got both of these today at the boneyard and neither seem like they will fit. I have a threaded hole and another small hole in the back of my heads but they are farther apart than the holes on the air tube and the bolts with the air holes in them won't fit. I have not got a good look at it because they are hard to access.

On my 79 there was also a large air tube going into the front right of the manifold, is this another option? Were there other ways that the air was injected?

The engine also smoked when they started it, it was about 90 degrees today and the truck was pretty warm, it spit out a lot more smoke than normal when it started and it was hard to start, not sure if that had anything to do with the failing, all the numbers were good though.

Any ideas would help, sorry for the long post.