Keep in mind that flippers weren't implemented until 1948 so the older machines weren't made with them. That caused the older non-flipper machines to become obsolete almost overnight and dropped profits for venders. Most older pre-1948 machines were fitted with after market flippers. There wasn't any standard for placement back then so they can appear in some strange places on the playfield.
I rebuilt my 1947 United Singapore and removed the 3rd party flippers.
That only leaves the careful skill of the ball shooter before release and proper nudging to avoid a tilt.
Most folks consider the old flipper-less machines boring but I personally like the challenge so I left the flippers out.