You'll need to be a little more precise with some actual measurements to be able to get a true number. First, you need to cc the combustion chamber of the head, you need to know the head gasket thickness, how much deck height the pistons have, and the bore and stroke. So to recap:
Bore size
Stroke
Combustion chamber cc's
Head Gasket thickness(actual volume will be more accurate to know on these gaskets)
Piston Deck height
Dome or valve relief volume(if true flattop with no dome or relief, then it will be 0cc)
All of the above values are required to calculate the compression ratio, so be as accurate as you can.
