Your gonna want to box in the frame any to mount the bumper,I'd like to see this thing in person, where abouts in B.P. are you?
that depends how much lift you have..mine had 6 and i never hit the tankIf you leave the front mount mount and move the axle back the 5 inches it will hit the tank for sure.
And the tank cant be moved back enough to clear (40 gallon) you will have to move the front spring mount bringing the axle back to the stock location. Buy doing that you will now have the front spring eye below the fram rail so it will drag on stuff and there will still be alot of rear overhang.
The main reason i wanted to do this swap and move the axle back because the tires where starting to get into the door 42" tires and the rear overhang was to big dragged going up and down hills. I could have lifted it more but dont want to go any higher than it is, actually want to lower it a couple inches. the other reson behind the swap was the 56 are going up front so i only had to buy one set of springs the 64 for $100.00 and will have a super flexy 4 inch lift actually came out to a 6 in the rear.
i would just keep the 56 in the rear if you are keeping it in the stock location do a shakle flip and in board the shocks plenty of flex and a ton less work.