Having a problem aligning the doors on my 69 c/10 how much gap should there be from the fender to the door to the cab  

Each truck will vary a bit but rule of thumb would be about a 1/4 inch. Just make sure to align the door to the cab first then align the front fender from there. You might also run into a problem around the window opening, because those are welded to the door and they could be out of alignment. Just align the main part of the door and if the window opening is not right drill out the small spot welds and move it into the proper position and reweld.