Not in a position to do that yet Sam, yes 69.25 will give 1159cc with a 73mm bore. Your measurement method presumes the piston is dead flush with the top of the barrel at TDC. I got the 1160cc figure from someone on the forum but somebody else says 1180cc which would be 70.5mm.
How r u Sam - might be giving you a ring soon - need some info.