How to get 400 hp out of 1971 340 .30 over

Is the casting modified by Allstate? Dig the removable air bleeds!
I believe so, from their website, 550 HOLLEY TUNNEL RAM CARBURETORS - Allstate Carburetor

Custom-built Holley 550 cfm carburetors. For Hemi motors, Inline tunnel ram, Jet boats, etc

550 HOLLEY TUNNEL RAM CARBURETORS. This is an unique set of custom 550 cfm mechanical secondary. These are only available here. These highly developed carbs are also the hottest set of tunnel ram carbs to date. Because of the design and claibrations the quick throttle response will throw you into your seat. Also they have a Very clean idle quality. YES they are MECHANICAL SECONDARY carbs. They are similar to the Holley 9776. Choose your finish from the drop-down menu. ACFI Polished finish as shown or the classic Holley Gold. All Non-stick gaskets and .110 adjustable needle and seats. Also featured in this set of carburetors are custom secondary metering plates. Because of this the secondary main jets are removable as well as the primary. Thus making these more tunable to your engine.

It took about a week and a half to ship once I ordered them. Two guys work there Jim and Jarred. When I called to order them they told me that they would have to build them before shipping.

Looking forward to seeing how they do this summer.