I agree on the plastifix in the painted areas.
If repairing a clear or colored lens in the visible areas is pretty much impossible. There are glues and products out there to glue them together etc. but most are for patching stuff together short term, not meant for "restoration" type repairs, most if not all of them will fail over time due to the hard/heat/chemical resistant properties of the thermoplastic that tail lights are made from not allowing a good bond in the first place. Even if they do work you'll always see the repairs. I'd suggest finding a better used lens to start with if you want to skip the $350 NOS examples on ebay/ 70/71 Duster lenses in good used condition are pretty common and not usually real expensive, they tend to have a pretty high degree of survivability.