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I don't think WD40 would do much to help get the emblem off. It will help get the adhesive off once the emblem is off, but I would use Goof off or Goo Gone for that.
I would use a heat gun or blow dryer to get the adhesive warm and then use a plastic puty knife to gently pry the old emblem off. I'm not sure ,but does the 79 emblems have prongs with speed nuts on the back like the stingray emblems do? If so, make sure to take the nuts off before trying to remove the emblem.
the side emblems do have prongs on them but when I took mine off they did not have speed nuts, just double sided tape. I have heard people using dental floss to get behind them. I was not worried about damaging the paint because I painting the car.
Pretty sure after mid 70's everything went to double faced tape. An infra-red bathroom heat lamp(with sunglasses) should help pull these off. Maybe a bit of light thinner clean up too. Find 3M Scotch-Mount Super Strength molding tape and some bench ex-acto knife cutting, puts things back quite well.
I want to restore all my emblems off my 79. Side ones look like double sided tape. Any trick what to use, without wrecking paint?
Why not order the assembly instruction manual (AIM) and read how they were installed at St. Louis. The process involved heating the emblem and the emblem tape. If you remove them, you probably will not be able to use the heat method to reattach them.
Have you considered cleaning them up with them on the car?
Unwaxed dental floss is the thing to use. It will fit into very narrow gaps; it is strong enough not to break under some stress; it cuts through tape fairly well. Tie off the ends to a couple of wooden dowels, then use it like a 'saw' to cut through the tape. You will quickly discover how taut you need to hold the floss and how much stress you can put on it as you are 'sawing' through the tape. Fairly painless process and it will not damage underlying paint. Use Goof Off or other solvent (like Prep-Sol) that won't damage your paint to remove remaining tape residue.