This is a big job and if you want to do it get a manual on it and do it right. You will need torque wrench etc. I don't know about thermogasket. There is a chance the head is cracked but it has to be checked when off.
Replacing the head gasket on any vehicle is a long and complicated process, however if you wish to see basic step-by-step instructions go to the related question on the right side of the page "How do you replace a head gasket?"
.044 inch , according to fordparts.com
A large vacuum leak can do that.
4:11 gear ratio
The fuse box is located in the footwell of the drivers side by the accellorator pedal. They simply pop out
1-5-3-6-2-4
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no ECM's in a 1981
Chevy didn't make a 1981 Celebrity
From the factory only one six cylinder was a option. 258 AMC inline six!
There is no computer.
If your 1981 Chevy V6 it leaking oil you can try simply tightening the bolts if they are loose. If that doesn't work then replacing the gasket is not a big job.