ok guys, so I have lowered cars before but not a truck.

I've owned this truck for almost a week now, and among the other issues popping up (freaking used cars man)
Is my suspension.

It's an 01 Silverado 1500 2wd and was lowered when I bought it.
Got it in the air today to start a tranny rebuild and noticed the springs looked funny and the shocks were leaking pretty bad.
Asked one of the older guys and he said they had heated the springs to lower it.
So, ok I know I have to go back to stock leaf springs and install a proper lowering kit.
Question is what else do I have to look out for? I've read about flip kits, and drive train angles.....
Also, is it ok to try and get some leaf springs from a junk yard vs ordering brand new oem or aftermarket?