While the port mismatch isn't the end of the world, an LD340 is still a "big" intake for a dual plane. This is only 273 cubic inches that has to suck through a larger volume intake. That's why I recommended an Edelbrock Performer or even a dual plane M-1. (Not sure how the overall volume compares between an LD4B and LD340.) Gotta keep the velocity up, especially on the street. What could be considered an "economy/torque" type intake on a 340/360 would be more performance oriented on a 273/318. Same principal applies to camshafts. What works best on a 340/360 would be bigger than needed for a 273/318 in the same application.
