When Chrysler did the 318-4 bbl package starting in 1978 in California, they used the 360 intake manifold, and a 360 size Thermoquad carburetor which was a mistake if you wanted the best low end performance. Chrysler knew better, but at the time the 2 bbls were atrocious due to lean calibrations, and a more enlightened approach using the TQ four bbl set up that adoped a stoichiometric approach to lowering emissions rather than a lean burn one (like GM did in those days), made all the difference in driveability, both cold and warm. But Chysler didn't want to spend the money for a 318 specific TQ and intake manifold, so the compromise was made. The 2 bbl guys had their head stuck in the sand using the lean burn approach which was a total failure and ended up with recalls. So some rogue engineers used the TQ to improve the situation (that is another story for another time). But I digress.
Large intake manifolds slow down the velocity of air/fuel charge into the engine which in turn decreases low end torque. And a carburetor that is also too big for the displacement of the engine is a mistake too. For the same reason. You need a carburetor closer to a 400CFM rating for a 318 if you want the best all around performance. That a 2 bbl was put back on the 318 you reference for better all around performance is no surprise.
