I might as well start on the bed build.
As usual, I couldn't make this easy. The bed floor is bolted to the frame, and I kept the front panel of the Dakota bed attached to the floor. That front panel is too wide, and it it too high, but I figured that would be better then too narrow and too short. The bed floor (except where the wheel arches were) is also too wide, trimming the width would also be required. I would also have to cut a notch out of the bed floor for the fill tube to come through the floor. The next thing is, I want the fuel filler tube to come up inside of the bed rather then outside of the bed. The original Dakota fill tube came up between an inner bed wall and an outer bed wall and filled through a gas door on the outside wall. This step side bed only has one bed wall, and it is inside of where the original inside wall of the Dakota bed was. The fill tube outside diameter is 1.75", to get that inside of the step side bed, I have to loose about 4" of its width, and still keep the upward curve. The top of that tube is about 6" above the bed floor, and there really isn't much tube that can be cut out of that height. The top of the tank is only 3" below the top of the floor and the fill tube enters into the tank at the top of the tank. I can modify the tube enough to get it inside of the step side bed, but making it shorter is a completely different story. I can build a box around the fill tube, and add the gas door to cover the cap. That will give the gas fill system protection from anything that may be put inside of the bed, but that presents another set of problems. The protection box will need to be removable, and the bed side will also have to be removable if there is ever a need to do anything with the fill tube.

If I make one bed side removable, I should probably make the other bed side removable as well, don't you think? I do. If the bed sides are going to be removable, they have to bolt to the bed floor and bolt to the front panel, and also bolt to the back panel. Most step side beds are welded together at the rear crossmember to keep them from flopping around, I'm going to have to add bracing at the rear some how to keep the rear of the bed sides from flopping around as it goes down the road, and those too will have to bolt in place.

So as I'm sitting and trying to figure out how to make the bed sides bolt on, it occurs to me the top of the bed rails are going to have to be pretty close to the same angle as the lines on the cab, or the truck will look "broken". That angle probably isn't going to match up with the angle the bed floor is bolted to the frame at. Maybe I can shim the bed floor to the correct angle, maybe not, but how am I going to get that bed rail angle right, and how am I going to determine how high the bed rails should be compared to the cab height? More thinking!

The 1st thing to do was determine exactly how wide I wanted the bed floor to be. I chose 49" because that was about the 49's original bed floor width. There were already enough variables, eliminating one of them couldn't hurt. The floor was trimmed to the 49" width (based off a center line), The area where the original Dakota wheel wells were will have to have 2" of gap filled in on each side. Then I added 1" to each side of the front panel (to bend and bolt to the side panels) then trimmed the front panel (based off the center line), and bent the 1" edges towards the rear. The original 49 bed sides bolted to the front panel, there were already bolt holes in the side panels I would reuse. With the width determined, I could clamp a piece of tubing on the rear edges of the bed, and clamp the front edges to the front panel, and determine the real height and angle I wanted by the old fashioned method, I stepped back and looked at it. At this point two more realizations took place. 1, Tire clearance was going to have to be cut out of the bed sides. 2, The original angles that Dodge used to set the bed sides onto its original floor had to be removed. After both of those were done, I was able to clamp the bed sides back in place. The clamping on the tube at the rear worked well, but the clamping to the sheet metal front panel and the sheet metal side panels left a lot to be desired. I came up with a plan. I could put a set of jack stands on the bed floor, then clamp a piece of 2" square tubing I had laying around to the top of the bed rails, then shim between the tubing and the jack stands until I got the front height I wanted. When I was happy with the angle and height of the rails, I could drill through the bent edges of the front panel through a couple of the holes in each of the bed sides and bolt the sides to the front panel.
Pic 1, Kind of hard to see, but you get the idea of the jack stands & tubing.
Pic 2, This is about how the tubing was clamped at the rear, the tubing pictured is 1.5" square, and the clamp was placed behind the stake pocket about there the chain hung (the chain was pulled out of the way). This was very stable.
Pic 3, This one shows the end result of this part of the thought process. I had a hard time trying to determine the height the bed rails should be, but then I saw the bottom of the cab and the bottom of the bed side and the light bulb went off in my head, why not line up the straight edge bottoms? Duh! You can also see the tire clearance cut out of the bed side, and you can see the clamp holding the rail to the tubing setting the front height. You can also see that the top of the rail pretty much has the same angle as the body line on the door, but is a couple inches lower. The height of the bed sides to the bed floor is different front to rear, the rear bed sides are nearly 2" higher off the floor then the front. Had I based the the rail angle off the bed floor it would have made the truck look like the rear of the frame was bent down just behind the cab, and it would have been a mess trying to lift the front sheet metal and cab, and the rear of the bed far enough off the frame to look right.
Pic 4, This pic was taken a bit later, but it really shows the jack stands/tubing/clamps to set the front height. You can see the fuel fill tube sticking up through the bed floor on the left side. This same set up was used at the rear to set the height of the rails there as well.