I put in a new line to the rear a couple of months ago and left the tank in place. I did use 2 pieces though. I was able to reach all of the brackets that held it in place.
edit: I did this in my 79 which has a different tank and skidplate from you. Although I still think you can do it.
79 cherokee chief
2" Body Lift
79 Wagoneer limited
78,79, 82, 87 all rolled up into one.