Exh manifolds in an Early A...

My son and I found and bought a set of exhaust manifolds on a 65 Dart with a 273 we are planning on using on his magnum swap since headers are just too pricey for this right now. We realize headers will be WAY better, but we're just trying to get this running for now.

We located some drivers side 72-74 340 manifolds on a couple of darts with 318's. Casting numbers checked out. Pass side are 318 castings.

1. Will the 72-74 340 manifolds "fit" like the 273 units in an early "A". They look very similar.
2. Safe to say the the manifolds from the 318 will flow better, even if slightly?
3. I can get them for $45 ea. Worth it?

Now, finally, we are using a 2.5" exhaust kit meant for use with heads and need to fab up some short pieces to go from the exhaust manifolds to the pipes where the flanges would normally meet up with headers.

If you've done this, what parts did you use or cut up to make up head tubes? They both will need a couple of tight bends it seems so I'd rather stack the deck in my favor of getting it right the first time if possible. Worst case, we'll use flex tube until we can do better but I'd rather not.

Thanks!