I'd rejoice if all my rockers looked that good! need a tetanus shot before climbing over some of mine
as for your objective to learn how to weld and replace your own, if you have a decent mechanical aptitude, I vote go for it..
I've had the skills since putting expert builder lego kits together in the 70s, been a heavy junk mechanic all my life since..
cutting, fitting, and welding steel is part of my trade.. only thing stopping me is time, and rust doesn't really bother me
my advice is similar to above, learn, practice, practice, practice..
practice cutting, fitting, and welding simple panels and slowly graduate to more complicated pieces..
if you have time, take some adult learning classes.. most community college classes are very affordable..
once you're confident you have the skills down, dive into your project..
and remember, you can make vast improvements although your first project may not be a show stopper..
these were production made trucks, they weren't perfect the day they left the factory..
and the joy of it all is that it can almost always be saved by more careful rework..
lots of threads here to guide you, may even solicit help from a neighbor or fellow enthusiast..
here's a fun thread caught my eye recently
Budget Shortbed: welding, grinding, rust oh my
good luck!