I like what you are trying to do here which is to build an accurate representation of Roth's pickup. I am also impressed with some of the detail work you have done so far. However the old Revell model has a few good parts in it, but the body, fenders and tailgate are so incorrect that it is about impossible to get an accurate 56 F100 out of it. There is an easier way.
Use the front and rear fenders, inner fenders, hood, tailgate and frame from the AMT 53 Ford F100.
Use the box from the Revell F1
Use the grill and cab from the Revell Foose FD100. (You can graft the back window from the AMT 53 Ford to get rid of the big window.
Use the engine, front suspension, running boards with a little modification, and tail lights from the old Revell 56 Ford kit.
You obviously have the skills to do this by the excellent work you have done so far.
If you are interested, I built a replica of a 1:1 56 I owned using the above parts. I talked about what I did to build the model with Doug Whyte for his Model Car Muse channel on U tube. The video is a couple years old.