Best manifold for ThermoQuad-equipped 340
The OE iron is a very good intake
There is a toss up between the LD-340 and the Weiand Stealth. I have not run the Stealth. I have run a LD-340 with a milled center divider and minor port work. VERY GOOD!
In the single plane world, the Holley Strip Dominator, then the MoPar M-1 which is a enhanced version from MoPar
Your looking for a street strip 12 second ride correct?
The OE intake is capable of doing so. You'll have an easier time with an aluminum unit though and the 2 dual planes should do it easy enough for you