In a Camaro, yes, October would be too early for a 307. I've never seen the data that Richard mentioned, but it certainly sounds accurate. But general reference, like Hooper, lists the changeover as 1/69.
You mention the present ME suffix, but no VIN on the pad. I assume the present motor is a 327. What transmission and what numbers on that? Is there an engine code with that ME? Richard is right: It is hard to "back into" what a car originally was without documentation. Post all the numbers you can find, trim tag and all.