I just checked my beat up, unrestored 70. I can move the trunk lid back and forth about an 1/8" only. 1/16" each way. It is a little clunky in sound as I move it back and forth so maybe that's what you're hearing. I should note though that I do not have the weatherstrip in place anymore which is why I can get it t move at all. I would think that with weatherstrip on, it should be tighter and not able to move by hand.
You might try closing the lid with slips of paper here and there around the trunk lid. Once closed, tug on them and see if any are loose. If so, I'd start there.