That original formular J B Weld will cure and be as tough as the auminum head, it's good to near 600 degrees as I recall, it just likes to cure slow so let it cure.
Coolant pipe ... There's a retainer at the back end, remove the hose and unfasten the retainer, the pipe slides off it's nipple towards the rear, it has two O-rings between it and the nipple that exits the back of the water pump cavity. If not rusty, it'll be OK but if rusty, etc, you'll need to remove the water pump (has it's own O-ring, no gasket) and take the nipple out the through that way, it's a press fit. I have seen guys knock it out but I have seen a engine block busted there too, so I'd use a large deep socket to receive it and threaded rod and nuts to pull it out slowly, and to install the new one. If not leaking, if no rust, if the car has had proper coolant it's life, I'd leave it be.
Edited by CrystalPistol (12/20/20 10:13 PM)
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