I used Seal-All, a hardware store contact cement/gas tank repair that will stick to almost anything. It sticks well to aluminum, and does fine with plastic, as long as you don't use so much that it attacks the plastic. It works on styrene, but if it stays "wet" too long, it will warp thin pieces. I never had any trouble with lenses i n headlights.
The joints didn't look good, but in the early 70s, I managed to glue KD MT-5s (now 1025s) to Con-Cor passenger car trucks with that stuff - and they held for years.