Some of the truck manifolds from the "Magnum" series engines do flow well. Not nearly as well as headers but still better than standard 318 units.
The 1992-1993 Magnum manifolds had a 2 1/4" outlet. The right side clears an A body. I've used them. They exit over and behind the oil filter. The right side is an excellent unit because it eliminates 2 bends and allows for a 2 1/4" or even a 2 1/2" head pipe with just a 45 degree bend when turning to run under the floor pan.
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The left side is always the pisser.
The truck manifolds might fit with manual steering but the column jacket will likely need to be trimmed. I ran a 68-71 340 manifold on the left side.
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The damn steering box is the main obstacle there. The options are an upswept design like the standard A body units or a 318-360 mid 1970s manifold that needs some grinding to clear the steering box.