What does that floor look like from inside? The following 4 pictures are with the cab sitting on blocks one inch above the frame, the intended finished height.
Pics 1 & 2 are the trans through the floor. The shifter on the trans is for the 4x4 transfer case. I should probably note that the flat part of the floor was patched at one time. Someone hacked in a 1/8" piece of steel from one side of the truck to the other. That plate is fit between the bottom of the firewall angle and goes back to the front edge of the seat riser. The hole for the trans to stick through took the center right out of that piece. I had to reinforce that entire area before I could put the new trans tunnel in the cab.

Pics 3 & 4 show the back wall and the section of the floor that needed to be cut out to clear the gas tank. The yellow strap is the strap attached to the Dakota tank that was used to hold the tank in place on the assembly line until the tank straps were bolted on. You can also see I also had to cut off the bottom of the cab support bracket. Originally the bottom of that support strap was spot welded to the joint of the rear cab panel and the floor pan. Originally it sat back against the back of the cab. You can also see the 1/8" x 2" wide steel flat stock I used to reinforce the back of the cab (in this picture the piece is just sitting in place). There is a 1" deep step down in the cab floor that originally ended at the front cut on the floor pan, you can see both ends of that step line still present. The oblong hole in the floor pan, just towards the front of the Dakota tank cutout was where the original gas fill tube passed through the cab floor. The original fuel tank on this truck was located inside of the frame rail, just forward (1/2 under the cab, 1/2 under the truck bed) of where the Dakota tank presently sits. There is a fill tube hole in the body, just behind the driver's door as well (you can see that fill hole in the cab side in the pic from the left side of the truck). The gas fill tube was filled just behind the door, and the tube passed through a rubber grommet, went through the cab behind the seat, and then passed through a rubber grommet and entered the tank on the front top of the tank.

Out of picture space. Next segment please.