[Smittee]

I used a Boyd's tank as well. It is designed to bolt up to the bottom of the frame rails. I did it a little different. I took three 3/8-16 Hex Couplings and cut them in half. Drilled holes in the tank mounting flange. Marked the top of the frame rail where I wanted the tank placed. Note: I had to remove the rear cross member but I didn't like the setup anyway. It had been taken out before I bought it and someone welded it back in with little clearance between the rear of the bed and the cross member. I fabbed up a new cross member that I can take in and out since it is now bolted in. Have to be able to take the tank back out for paint!
I then marked the holes on the frame rails and welded the hex couplers in place. Plan to use stainless bolts and a rubber spacer between the coupler and the mounting flange. I think I gained about an inch and a half or so. I haven't put the bed back on yet so i am not 100% sure what will hang down. You can look on Boyd's Welding website to see photos of some installs though.
I will try to attach a few pix.