my thoughts...
> What would you do with it?
Good question... with the super narrow width it might be a good mud rig... less drag. I'm always leaning towards trail rig builds though.
> Tube chassis or chevy frame?
Chevy frame for sure...
> Link it or leaf it?
Link the front for awesome 90-degree-plus approach angles... super long leafs in the rear, 64s.
> Flatbed or box sides?
flatbed.
> Doubled or not?
Depends on the engine... with a hot 383 a single t-case might work fine... especially if it had good axle gearing and a t-case like a np241 or something with good low gear. You said ya have some 241s laying around.... they are a pretty good case and would keep overall weight down too.
> Exocage maybe?
yeah, gotta have something! Prolly gonna start running our of room quick on the inside if you did an interior-only cage.
> Axle selection?
How much $ you got to work with and which tires do you wanna run? Lookin' at the stuff you have on hand, I'd go with the hp d44. Keep the rig light as possible... and an appropriately light tire selection... like 37s-38.5s on some aluminum rims. Keep that rotational mass down.
> Build on the cheap or extreme?
That one is up to you.

I always enjoy seeing cheap-parts-but-awesome-fab-work rigs... those are the best buildups. The $200,000 uber-comp buggy build is actually pretty boring IMO. Yes, the end result is good... but for the price is sure as hell better be too. Also, there is nothing more funny than some guy in a rig he threw together for $5,000 kicking ass all over a $40,000 luxury SUV on the trail.
j