I just finished doing this... get yourself some penetrating spray and apply liberally, and let sit for a bit before starting.
The crossover pipe isn't that bad. You'll spend more time lifting the car so you can get under it.
The studs on the head
/header are 14mm, but you will need a deep socket given how long their ends are. You'll also need a deep 13mm to remove the nut securing accessories to the bolt in several places.
I believe the actual upper header bolts have slightly longer studs than their bottom counterparts. Just compare them as you take them off to make sure they go back in the right spots.
I didn’t need to remove the wheels, but I already had the AC shield, plug wires, and down pipe out of the way which helped. A ratchet with a break over head and maybe a short and long extention will help more than anything. That type of ratchet is usually longer too, which will give you the leverage to break them loose.
As far as the exhaust gasket, the general concensus is not to use them. I had one person tell me it could actually do more harm than good. However if you have the crack welded it should be bolted to something to keep the heat from warping the header.
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