They functioned in an entirely different way.
The carrier was similar, but rather than a hammer, there was a striker that rode in the back and took place of the buffer, and then there were nested springs that shoved that forward.
If you're intent on going completely correct, it'll take a lot of doing. Parts are near-unobtanium. I know a couple of the buffer tubes/caps have made the rounds. I have a tube, but no cap for it. The springs are likely unicorn beaks, at this point. I've seen a carrier/striker set go a few years ago.
Most of us just have one of JHud's kits, which use a spring of his own manufacture, as well as a chopped down buffer.
Edit: For whatever it's worth, Augee has a fantastic, photo intensive teardown of a real M231 that he had in his unit, here:
https://www.ar15.com/forums/t_3_123/459672_M231_Firing_Port_Weapon_Review________56K_MASSACRE______________.html