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If the only thing that was done was to add another exhaust pipe flange, that manifold is junk. The correct way to split an exhaust is to add a divider that almost, but not quite separates the runners into two segments, and add the extra flange to the rear section of the manifold behind the heat riser area. Leave about a 1/4" slot above the divider to allow a little circulation between the two halves while the heat riser is in the "closed" position. The idea is to split the exhaust into sequential pulses that alternate from one pipe to the other. Done right, it creates a very distinctive exhaust note, and just might create a tiny power advantage. It's mostly eye candy to impress at a show and shine.
Jerry

OK thanks. In your opinion, what is a good header option and keep just 1 carb?

This? https://www.googleadservices.com/pa...VcFFkFHdyzCnkQ9aACKAB6BAgFEBE&adurl=

Now before I suggest anything, I know that several of our members have installed these headers with no notable issues. If you live where it’s hot, this may be the case. If you live where it’s cold and plan to drive in the cold, this will not be the case

Now with that being said, the issue with adding these type headers, is they don’t heat the intake manifold really well like the heat riser does. This can result in drivability issues when the engine is initially heating up due raw gas not being vaporized in the intake manifold by the exhaust heat. This happens pretty fast with the heat riser in the closed position. Once heated, the heat riser closes to prevent overheating.

In addition to the headers, you will need to buy a plate to close off the bottom of the intake manifold. This plate has two ports that you would hook up either heated water from the cooling system or piped directly to the ports on the headers.

Both of these heating systems work to a point but no where near the original heat riser. If you go the water heated route, it takes longer to heat up but is a more even heat. If you heat with the exhaust, the heat is quicker, but with no way of shutting it off.

The best way, is to buy an original corvette exhaust manifold if you can find and afford one. While your at it, get the mating corvette intake manifold with three carburetors. That is the ultimate setup. Be prepared to open your wallet really, really wide!

You can always fabricate one as HRL has suggested OR, Just put on the spare stock manifold you already have!

It would be hard to chase me fast enough to give me anybody's aftermarket header system, when it's so simple and inexpensive to split a stock exhaust manifold. That also retains the heat riser system that the engine was designed to have in the first place. The only difficulty is in finding someone who can weld cast iron, if you're not able to do it yourself. Recently, I bought a roll of nickel-alloy MIG welding wire, and I'm going to be experimenting on a few junk manifolds I have sitting around to see if I can do an acceptable job of splitting a manifold that way, rather than using nickel rod and a stick welder.
Jerry

I`ll separate the 2 manifolds and headers and take pics of them.
I`d be in favor of using the 2 best. The one modified looks like the heat riser was plugged.

Are the Fenton headers any good? Fenton | #91013611
Fenton® 1936-1959 Chevy 216/235/261 6-Cylinder Cast Iron Headers

Basically the same as you linked but made of cast iron. Still the same issues.

Here are my choices. The blue manifold looks good.
The 2 headers both have issues. The original ,(no extra flange) just needs to free up
the heat riser. Fingers crossed. And 2 mounting bolts for the pipe.
The modded one has no heat riser and pretty well pitted. Maybe more problems.
Any good options there?

Painted the engine. Turned out good. GM Blue. Funny how the flash makes the blue different.
Thats the best she`ll ever look. It will go in this 58.