Fuel tank install ????

[muckyp]

I was so pumped this morning as I was finally going to put the bed on my truck, only to be quickly let deflated. I bought this truck with what I believe was a Blazer tank already installed, but with no truck bed. I am now attempting to install the bed and the rear most bed rail is hitting the tank. I know that the Blazer tank install is a very common upgrade, but I have searched and can't find where anyone else has had a problem with the bed hitting the tank.
Am I missing something? Is there some modification that people are making to the bed for the tank to fit? Any help with this problem would be great.