I repaired my 73 front end with more damage than that by using Epoxy fiberglass resin (not polyester, vinylester anything ..ester) and medium filler cloth.
1. Clean the hell out of the part to be repaired and cut some pieces of cloth just over the size of the repair required.
2. Lay some resin down with a brush. Not too much at a time.
3. Then cut small pieces of cloth and lay one bid (layer) of cloth over it.
4. Nice soft strokes of the brush with more resin on it to get the cloth to lay down flat. Keep the brush wet with resin.
5. Poke at it a bit with the brush as you must get the air bubbles out.
6. Keep filling out with resin and cloth if you have to extend the repair past the original part but look at the cloth weaves, you will see how it is oriented and place the weave 90degrees to the first cloth install. Don't put too much on at once, wait 12 hours before doing it again.
7. Once you have your shape you can sand the resin and cloth down with coarse sandpaper then go the bondo route.
8. If the skim of bondo is light (IE you did a good fill job with Epoxy and cloth) you will never have a problem with cracking.
9. Also put one layer on the backside to offer some more strength - the spot where your picture shows it a little crummy.
10. Remeber keep it thin in case you apply another layer.
Hope this helps. It worked on my car and has worked on my airplane for 4 years now and that thing sure vibrates way more than a car and zips around at 180-190 mph in cruise and no cracking.
