Gil,
My own personal experience has been that an intake charge does not like to turn a 90 degree bend, regardless of the motor or the installation. Yes, the 40DCOE/PBS intake manifold will work (looks impressive too), but it is probably not the best carburetor intake manifold combination for this style of head.
There are a number of better performing alternatives. In the main a two barrel downdraft combination will give a better airflow. For years the favorite has been the 36DCD type carburetor [two versions a) progressive linkage b) non-progressive linkage]. This carburetor with 29mm venturis is a good combination. For all out racing, the non-progressive is preferred, however for street applications the progressive type may have the advantage with somewhat greater economy at part throttle and the same performance at full throttle.
Weber makes another series of carburetor referred to as the DCN series. This can be anything from a 36DCN, 36DCNVH, 40DCN, 40DCNF, even a 42 or 44DCNF. Keeping in mind that the 29mm venturi will determine the actual airflow through the carburetor. This carburetor requires different intake manifold as it sits in-line with the cylinders. Some say that the carburetor starves for fuel on right hand corners, but this is sort of an urban myth. With the float level properly set, this type of carburetor works very well.
FInally, there is the Solex 40-42 CCH. This little known and regarded carburetor was made by Solex in the 60s-70s purely for motorsport applications. It is very basic, but very effective. In addition it is cast in aluminum, versus the zinc alloy used for most Webers, so weighs considerably less. (Note: Some DCN Webers for Ferrari applications were made in aluminum as well). It was used on German Ford V6 motors extensively as well as by Saab on the V4 powered rally cars. It has replaceable venturis similar to the Webers mentioned earlier.
All three carburetors have a four circuit configuration consisting of an idle circuit, a cross-over circuit, accelerator circuit and a running circuit, so tuning is pretty much the same.
All of these can be fitted to the Fiat 850/A112 type head with the correct intake manifold.