Original poster, that looks like a Hitachi two barrel, probably the smallest of progressive two barrels used on early Datsuns. Same design was used on many Subaru and Mazda but with larger venturi. The smallest version was a 20mm primary venturi with a 26mm secondary venturi. It should be stingy on fuel but have a decent punch when you crack the secondary. The small venturi should help keep the mixture moving faster through the setup. Like any conversion, some tweaking is likely necessary.
I am not a fan of the log-type manifold but there are lots out there. To me there are too many places where fuel could pool and cause a potential explosion. A few, quite a few, guys have made them from PVC pipe. Some have exploded. No one hurt, just extra laundry.
The ones using a VW type two barrel collector probably are safer as everything is sloped towards the intake runners and if the mixture is too rich, fuel wouldn’t have as much chance to pool enough for the above mentioned kerblam.
Another potential advantage would be ramming effect of the longer paths and an increase in bottom end torque. Would the average rider feel it?? I doubt it, but maybe.
I have two of those carburetors and a wild fantasy of using one on each side. Two years now and it all sits in a box in the garage.
Leaving the original Goldwing carb design out of the discussion, the single carb should see a steady flow through its venturi since the four cylinders take their turns pulling, 1 then 3 , then 2 and 4. The intake valve is open 235 degrees on early models, each intake opens 180 degrees apart, so at some points, the one carb is feeding two cylinders at the same time, but with a single carb the flow through the venturi stays in motion. Slight pauses in flow, but not as much as the stock setup whose venturi see a flow, and then an abrupt stop when the intake valve closes for 485 degrees crank rotation.
Using two carbs, like my fantasy, I will lose the advantage of continuous flow. 1&3 will pull, then a delay of over half a rotation (250 degrees) as 2-4 pull their charges in.
Another comment on the Hitachi carbs. The pic looks like a new knockoff. Cheap knockoffs are available new for just over $50 from China. I bought two. Pulling them apart I found numerous chunks of casting flash and drilling remnants. It would be worth the time to go through it to ensure there is nothing to plug stuff up when these pieces let loose.
There are a few versions available. I went with a standard cable choke but an electric choke is available. The early ones use a counterweight to assist second barrel opening up. I removed it to increase flow capability.
They would be fairly easy to rejet as the top comes off like Weber and others. Two are from the bottom, so proper placement so they can be accessed will aid dialing them in.