Since you arent going to be using the old springs again just cut the spring off with a cutoff wheel then you can get to the bolt holding the retainer plate from the bottom side and that should simplify matters tremendously.
Also those springs probably werent heated.
Granted they appear to be sagging but Chevrolet used a progressive spring design and the middle 3 coils are usually compressed together when the truck is sitting on the ground.
If more coils then that are compressed under the normal weight of the truck then yeah he probably heated them.
Its more likely that they are just worn out and really are sagging naturally.