Well, first of all, you can't make a 327 from a 305. They're two different block castings.

327 = 4.000" bore with 3.25" stroke
305 = 3.736" bore with 3.48" stroke

Just about the largest you could make a 305 is a 315, using a 0.060" overbore.

There is a way to measure cubic inches without disassembling the motor. We do it all the time at the drag strip with a P & G cylinder volume tester. Check around at some of the circle track racetracks or dragstrips in your area and inquire if they can "pump" your motor.