Eventually I settled in on the GM/Chevy extended cab proportions and also firmed up what chassis I was going to need as a donor vehicle. By then I had bought the two IH trucks and started to realize that before I cut them up I'd better have a more accurate idea of what dimensions worked. I realized the photo chop stuff could be out of scale enough that it would really mess me up.
So I moved into using Solidworks instead of Powerpoint and started making accurate measurements and scaling better. If you haven't guessed already I am an Engineer so I like having numbers to go with my ideas. This is where and how I finalized my plans and decided how big I wanted the rear door openings and the length of the bed. Here's a pdf file that shows an example of the "engineering drawing" I am using as a guide. (Warning - these dimensions are not my final ones so don't go cutting up another pair of trucks off these!)
