273, or 318?
There are no numbers to match in a 67 car. Numbering the block with the cars VIN didn’t start until the middle of 68, and across the board in 69. That being said, if the cylinders need to be bored to correct one cylinder, you will have no choice but to use aftermarket pistons for a 273 with an overbore. You can however, have the offending cylinder sleeved and use the stock pistons if the other cylinders check out as ok. That’s what I would probably do, I have a few cars running 273’s, and they’re a great little motor.