Very cool car to find and bring home. Not at al unusual for a '66 Chevelle to be rear-ended. The tail lights are very sexy, but not very efficient. My dad bought one new and it was tagged twice in the first 5 years. It had a manual trans too and when we were sitting, waiting to make a left turn, we learned to NOT angle the car to the left at all, or the tail light wasn't visible from behind as it blinked. We also tended to keep our right foot on the brake for the right light to illuminate. Having the left side replaced seems to be the most common rear end side damaged.
I don't think I would attempt to turn the engine over in the car. If it has been sitting without a carb that long, there were probably mice in the intake/heads. I would haul it out and disassemble it to inspect and clean. If all looks good, re-assemble, as is, and fire it up.
And, when you are tired of cleaning and inspecting and don't have more time for it...
