bed swap stepside to fleetside

[Pugster70]

I bought a stepside truck and am putting a fleetside short bed on that frame . The bed sticks up alittle higher in the back than the front , the cab to bed body lines line up at the bottom. But the bed is alittle higher starting at the wheel wells, it's about one inch higher. I want to make the bed even do I need to cut the pads off the frame and make them smaller for the bed to set level on the frame. Anyone know how I can fix this problem?