headers in the states I have a nissan motorsports header I may sell but it may not clear factory intake it was designed to be used mikuni dual carb manifold. there is also one for sale on ebay

I think that there is a bush in the hole, so you might need to push it out. I don't remember how hard this bush is, but something tells me that a drill is not going to do the job either.
The bush is made of a dis-similar metal to the cast, so trying to weld over it with the proper cast iron rod might be a problem.

Forewarned is forearmed.

It must be open ... it should only be closed for about 30 seconds while the engine is first started. You don't want to block your exhaust system.

You could take it out, or just wire it from the outside so it is stuck open.

Leave it ALL OPEN and weld it all around so it won

These things are a pain when the shaft or bush becomes worn & the noise from the leaking manifold is irritating.

Interestingly, The A10 engine in Datsun 1000 coupes, & only the coupe version, did not have this flapper valve. They also used a free flowing dual outlet exhaust manifold.
This manifold also bolted to the inlet manifold's hot box in the same way as all the others & presumeably provided enough manifold heat, but without using a flapper valve.

If you live in a warm climate area, then removal of the flapper valve & shaft should not cause any real hardship.

Looks like a 1971 manifold (1973 has cast cooling fins).

By "baffle" do you mean the flap valve (heat riser)? If this valve gets stuck partially closed it causes the manifold to overheat.

Even in normal operation, the valve shaft can wear and then blow out. Lubricating this every 12 months is part of the Periodic Maintainence of your 1200. See "exhaust manifold heat control valve":


wiki - Owner's manual

that flanges is the one that bolts to bottom of intake coerrect? if so and you weld it, you want to weld in a position to limit exhaust from bottom of manifold for a cooler intake charge.
best solution is to replace manifold with a exhaust header.