Spent most of the day removing all the parts and junk from the panel and then sweeping it out. I uploaded new picture of the interior and the pile of stuff that was inside.
http://s257.photobucket.com/albums/hh206/sfeldma/1954%20Chevrolet%203100%20Panel%20Truck/We made two piles actually. First pile was everything we recognized as parts from AD truck/panel. Second pile was everything else. It was about a 50/50 split between the piles, so I got some good parts to work with or trade. I not sure what to do with the other pile. Anyone need a drive shaft from a '69 olds 442?

All kinds of random stuff was in there. The drive shaft was marked, but most is a mystery right now.
The floor was in really good shape and the inside walls look very good. A few dings on the inner rear fenders. The bucket seats are cool. Pretty much shot on the business side.
I would say the truck raised three inches with all that junk out. I peeked underneath and the rear springs have this funky overload spring that fits on top of the axle and under the frame at the high point. It's hard to describe; not sure if it's stock or aftermarket. The gas tank looks newer and my dad remembers the seller mentioning it was replaced. The front end is real tight. No play at all in the steering. The seller said he had new oversized king pins put in and they must have tightened up the other steering components.
Ran out of time to look for the engine markings to figure out what I have. Thanks tclederman for the info/links.