Engine too loud after head work and lacks power

I posted earlier this year after I had my 250 4.1 head machined and grinded. The engine was overheating and had no power. I suspected that the machine
shop did something wrong but I found that they did everything correctly. However, the engine is now too loud. When idling the engine sounds ok but as soon as I start driving the engine is too loud. I did not install the exhaust flange metal ring that goes between the exhaust pipe and manifold. Could this be the problem? Also, the engine would not idle at all after the choke came off. I had to reverse the 2 carburetor screws just to get the engine to idle. I realize that the throttle plate is now open wider that it used to be but I can get a steady idle and steady timing and can drive the car. The engine lacks power which is really apparent when starting out from a dead stop and going up hills. Any ideas would be appreciated.
Thanks in advance
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You say, "too loud." Can you please describe how the engine sounds?
What did you do to try to diagnose the problem? Can you feel gas coming out around where the exhaust pipe and manifold meet?
I don't know if that is the problem, but, it is a problem. You're going to have hot gasses that contain carbon dioxide and other fumes leaking out under the truck. That can easily get into your cabin. Let's just say that is not good.

I can't help wonder if there is a timing problem or if the timing chain is off by a tooth. Something like that would be my best guess.

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You mean the doughnut shaped gasket about 1/2 inch in diameter? Yes, that would let your engine roar.
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I have two different exhaust flange gaskets for the car. They are about 2 inches ID. One is solid metal and the other is some kind of material. I tried but couldn't align the exhaust pipe with the gasket and manifold flange. I will go ahead and install it somehow even if I have to remove the catalytic converter.
The manifold broke at the flange back in 1993 and I had all the symptoms then that I have now: loud engine and loss of power. That is why I suspect something with the exhaust.
Thanks for the help.

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