CO2 motors are still made and sometimes very cheap on e-bay. The hard part is finding the right size CO2 cylinder to fill it. They typically call for a size 2/3 what is used in Crossman CO2 pellet pistol.
Usually they are very small motors. About right for a 12-15 inch span FF model.
I'd save the antique motor and if you want to experiment get a modern one cheap. The good quality ones are not so cheap... but a lot better than the antique.
Looking closer, I see parts and instructions from at least 3 different models in the box with the CO2 engine.