Which manifold gasket to head is best?

The metal gasket is for a center mounted carburetor- you're trying to conduct as much heat into the manifold (and even some into the carburetor) as possible to keep the fuel in suspension.  Use the fiber/composite gaskets for dual carburetors and manifolds to keep them isolated from head heat as much as possible.

Thank you. Any suggestions on what jetting is needed with my plugs are black? I am running dual Idf40 Weber’s from Spain?I currently am running f11 tubes, 50 idle jets , 50 main jets and 115 jet in the bottom of the f11 tube.

The 115 jet in the bottom of the F11 emulsion tube is the main jet. 50 idles and 115 mains come stock with Weber 40 IDF carbs.

So it is safe to say your carbs were never jetted for your engine.

Without COMPLETE engine specs, nobody can give you a jetting suggestion. And that will only be a suggestion, it may/will be off at best.

Do you have access to a wideband O2 sensor? The reason I ask is reading plugs is very iffy with today's fuels. Your plugs will be black if you spend a lot of time idling and/or never really get the engine heated up.

To really read plugs you have to shut the engine off at WOT(wide open throttle) UNDER FULL LOAD above 3000 rpm, then pull the plugs. If you run the engine normally after and cruise into your garage the reading is useless.

Anyway, the wideband sensor can tell you what you need to know. It can help you choose idle jets(idle and low speed/low load AFR(air/fuel ratio)) and main jets(above 3000-3500, cruising or WOT). After you get the right idles and mains, you can go further into air correctors(in the top of emulsion tubes, under the jet holder) and possibly into different emulsion tubes. Float height changes the mixture too. The absolute LAST thing that gets adjusted is accelerator pump squirt.

ALB has covered the intake gaskets well.

Thank you for the information. It is very helpful to understand the workings.