Well, there is about 8 gallons of gasoline on my driveway this morning (66 Valiant)

the hardest part is the "J" bolt usually has undercoat/rust & is a bear to remove.
everything is straight forward---- the seal will probably need replaced around the filler neck.
the ground clip will most likley break when you try to remove it-- the part wedged to the frame---
Is it leaking from said repairs-- or has the cold weather brought about a new leak/seal problem?

Someone hear should have a decent used tank-- good Luck ,Lawrence