I would be most concerned with the brake line if your fuel lines are in that condition...when you need the rear brakes...that line might be in jeopardy....and the top side of the sub frame between the floor pan is a moisture trap that rotts out the lines after all of these years...

removing the rear sub frame is not hard work, it takes two people and a jig to make it easy...and a good weekend of time....

the dealership can sell you the lines you need 80% pre bent at a great price...

good luck - be safe
Jake