Need to replace the 1/4 panel extension on my '72 Supreme and was wondering if I need to loosen up and lower the rear bumper.

 

You should not need to. A couple of nuts on the inside of the trunk hold it in. The small black molding between the extension and the bumper could come out to give you a little room. (or they will fall out...)

 

You mean the bumper filler?

 

Yes