The injection blow molding machine of this invention has a small indexing plate to which heads of different size can be connected. A small head can be used for long core rods when making parts of long length. Larger heads are connected to the indexing plate for accommodating more and shorter core rods. The same machine can, therefore, be used for making different parts of a variety not possible on standard injection blow molding machines. Special features of construction prevent the blowing air from exerting an upward pressure on the head that carries the core rods; and an improved cam mechanism operates air valves without exerting side thrust against the head. An indexing alarm prevents operation of the machine when not properly indexed at the operational stations.