Buying a car without keys

A question along the same lines of the gent that started this thread.
I bought a 67 barracuda from the original owner who was in the middle of a move when he sold me the car. He’s sure he has the keys but has yet to find them as he unpacks boxes.
I would love to get into the trunk but I don’t want to drill the lock as I’m still hopeful he will find the original keys that came with the car on day 1.
Is there a way to open the trunk on a fastback barracuda without a key?
Is it possible to get in through the back seat or are you locked out of the interior, too? I couldn't do that in my case because the trunk was jammed full. You may be able to break in to the car, then go in through the back seat.