You must live in the south/west if you call that a LOT of rust!
Over here, we'd label that one somewhere between 'almost no rust' and 'just starting to rust'.
Those are the common rust areas - look up on LMC Truck parts for the weld in patch panels.
Not sure about that year, but I'd be surprised if you couldn't find them.
I'd say as long as the frame is solid, you've got little to worry about.
Yeah, it'll be a money pit, but... what isn't?
It's the usual situation - you'll always spend more on restoring something like that yourself than you would buying one that somebody else restored.
But - how much more? A couple grand?
There's something to be said for doing all the work yourself. Not that you can do it better or cheaper - but you get intimate with the vehicle. You learn ever inch of it, and know it inside and out.
That can make ownership much more enjoyable - when you hear an odd noise you'll know what it is and whether or not it needs fixing.
Where if you bought it restored, you always have that worry - not really knowing what's inside, or what's about to let go...
Bottom line - if you're looking at it as some kind of investment - forget it.
Go into it knowing you're going to end up about $8000 poorer for it (much more if you want a show truck). It's the price of happiness.