I was out taking measurements tonight of the floor pan shackle holes to floor pan edge, compared the left and right shackle dimensions and measured the distance from the frame to the holes and all looked spot on. The shackle holes in the frame on the side with the biggest gap are about 3/32" higher than the low side. That is a minor contributor in my eyes. Not aircraft tolerances but good for its time!
I attached a couple photos showing the gap difference with respect to a planed piece of wood that is about an inch high.
The picture with the piece of wood under the cab on the passenger side corresponds to the picture of the shackle with all the shims, lol. The ply wood in the gap is 3/4 and I probably added another 3/8 to get the holes to lineup in the cab. The picture with the piece of wood running up against the back of the cab is the driver side.
I will take another shot at it tomorrow night with your suggestions and let you know how I fair.
