Can a stepside bed be shifted/centred?

[70StepsideC10]

I searched around the site but could not find a definitive answer to my question. While measuring the rear of my truck for new wheels and tires I realized that the stepside fenders are not centred over the wheels left to right. What I have found is that the rear end is centred, the box seems to be close to centred, but the driver side fender sticks out further from the wheel mounting surface than the passenger side. The fenders are aftermarket, installed by a PO during the restoration, and it appears that the driver side fender is 3/4" wider than the passenger side fender. As a result, the wheels/tires do not sit evenly in the fenders, the driver side is sunk in a bit and the passenger side is pretty much flush with the edge of the fender. Is it possible to shift the entire bed assembly towards the passenger side so that the fenders appear centred over the wheels? I would only need to move it about 3/8" to accomplish this. I know this doesn't seem like much, but it is rather noticeable. There are 8 bolts that hold the bed on, and I took a look underneath and it doesn't look like the holes are slotted so not sure if the bed can be shifted.