If the motor is original its not a 327.
There should be a number stamped on the block just in front of the passenger side head. If you can find and read that number its possible to look it up and determine what the motor originally. I've found these codes on the web before, but don't recall where.
Otherwise you're stuck looking at casting numbers, which should narrow it down too. Casting numbers can be found at
http://www.mortec.com/castnum.htm.
