I've got an LD4B. I was told early on (here on FABO) that it's a good intake. Now, I don't know much about engines on a theoretical level. What's the deal with dual plane intakes? Longer runners?
The LD4B is the best street intake for a 273/318 as it has the smaller ports to match those heads.
When my son first bought his 71 valiant with a 318 performer intake and Holley carb, we changed it over to a LD4B and Edelbrock carb and it ran much better. Stronger coming off the line with no bog. We didn't do much tuning, pretty much bolt it on, set the idle screws and run it...
It's a much better intake than the edelbrock performer...