Polaroid camera's can take ND-filters which allows a SX-70 camera to take 600 film.
A filter helps with the amount of light that the camera provides - this amount should match the amount of light that the film needs.
Below you'll find some information to think about while shooting with a filter.
SX-70 film is a slow film that needs a lot of light. It needs four times the amount of light of a 600 film. Consequently the SX-70 camera provides four times the amount of light to a film than the 600 camera does.
You can put a ND-filter in front of a lens or in between the lens and the film. The 600 film will see four times 1/4th, which is just the right amount of light