Ok, now you're getting really technical on me. How does removing the divider give you more HP at higher RPM? 
Dual Plane manifolds are designed for better low-mid range and single planes for higher range RPMs.
Removing the divider moves the power band higher by making it act a little more like a single plane intake.
It's a slightly modified 340. I'm changing over the car to a shaker and in my research the LD340 is the one that will fit best with the shaker and not be too much or too little of a gap. I would rather have to add a spacer than to figure out an alternative.
Is it going to make that much of a difference with the center cut out?
You could lose a little torque in the bottom end and gain a little HP at the top end. Again, it all depends on everything working together. Carb, Intake, Heads, Cam, Headers/Manifolds...
There are quite a few known combinations that will work depending on what you want it to do. I just told my engine builder what I wanted and he exceeded my expectations.
We put several different size spacers on my stroked 340 [418 C.I.] on the Dyno. My engine did not like any of them... it made less power and less torque with every one of them.
