I think the 68's use a similar "banana wrap" like the 70's vintage.
You can remove it by taking the blue vinyl strip out of the aluminum extrusion, ( might have to remove a screw or rivet at the ends first) Drill out the rivets in the extrusion, remove the extrusion, drill out the rivets that hold the wrap to the upper shell and the belly pan. Then is should come off, but there may be a rivet concealed behind the next wrap. After you finally get it off you can GENTLY!!! start at the outside edges of the dent and press with a rubber covered hammer handle, it takes a while and you want to work it very slowwwwly so you don't stretch the metal. I have a fair sized dent in mine also, you can see it by clicking on my photos button at the bottom of the post. At the moment it is the least of my worries.