7A-FE Header, Confirmation on thoughts needed Options

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I'm trying to figure out what to do exhaust wise. Had taken the heat shield off to paint it, and found 3 cracks in the exhaust manifold. None of them are all the way through yet, but figure it's just a matter of time at this point. Of course all of the headers available for the 7A-FE throw everything off: upstream O2 sensor doesn't read off all 4 cylinders, removes the catalytic converter below the manifold and then would throw off the downstream O2 sensor reading. Only other option would be to get another cast iron manifold. Then again could probably get a 7A-FE header then modify it into a 4-1 coupler and put the O2 sensor port on the coupler. That way could maintain the rest of the exhaust and not worry about throwing codes. Though from what I've read by searching on here, being it's OBD-I removing the cat between the sensors shouldn't throw a code. Being this is Alabama, emissions testing is not a concern. My concern is throwing the computer off, and hindering performance/economy instead of helping it. The cheapest cast iron manifold I've found is $90.86 shipped, where as I can get the header and down pipe for $58.90 shipped. Not only that but I get money from scrapping two cats by going the header route. So you can see my dilemma at hand. Another thought I had would be to remove and patch the O2 sensor port off the header and put the port on the down pipe, connect the secondary cat to the end of the down pipe and relocate the downstream O2 sensor behind that cat. Thereby emulating the current factory setup. If anyone could shed some light on this it'd be greatly appreciated.

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What I'll end up doing I suppose once the manifold finally cracks through. I'll plug the O2 sensor port on the header, and put one at the soonest point where I can get a read off all 4 cylinders. At least that way the reading between the upstream and downstream sensor will be the same. Then lots of straight pipe, and a muffler.