jrjr, atleast on my truck when I did my lift, all the bolts slid out except for one (drivers side, forward, upper bolt). If they are stuck inside the joint after getting the nut off, I would take a piece of wood or brass stock and put that on the outside part of the bolt and then using a hammer, beat the bolt till it is flush with the frame. From there, you can take a punch and push it the rest of the way.
As for the one bolt that you can't remove due to the gas tank being in the way, you have 2 options. 1) you can drop the gas tank, ROYAL PITA!!!!!! or, 2) like was mentioned, use an angle grinder and cut the bolt head off and then pull the remaining part of the bolt out of the joint using a pair of vice grips or the like. Sawzall works, but takes a lot of time. Angle grinder is better, just don't "slip" and have the grinder get into the side of the gas tank.