If you can, trial fit the manifolds on the heads with the engine out side the car. There is a high probability that the drivers side dump tube will hit the boss on the head where the air injection hole is and not lay flat, causing an exhaust leak. Don't ask how I know how hard it is to grind it off with the engine in the car!
Also, if you use the factory studs to mount the manifolds, eather pull them (the studs) out, then pull the steering column, and then set the engine in, or pull the steering column out and put the manifolds on and then set the engine in.
It's been awhile since I worked with stock exhaust in an Early"A", these are the things I remember.