I agree with Dave @HeritageCameras that this lens likely has a Canon FL mount. The reasons are as follows:

• It has a breech mount. Canon FL/FD lenses are among the most well-known breech-mount lenses.
• The location of the pin matches that of Canon FL mount lenses. (Circled in green.)
• The lens has screws that match those on known Canon FL/FD breech mounts. (Circled in red.) These screws fit into a notch in the FL/FD breech-mount lens cap. (Circled in blue.)

You can easily confirm the mount by attaching the lens to a camera with an FL mount.

If you are looking for an adapter, it is compatible with the Canon FD mount using stop-down metering. See Evolution of the Canon FD Mount.

If you'd like, you can measure the mount diameter to compare with a list of lens mounts (alphabetical, by-register, Wikipedia).

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The pin on this lens is not longer than the pin on any other FL or FD mount lens. It only appears longer because of perspective:

• The lens is being held with the front element away from the camera. Note the extreme converging lines of the lens barrel.
• The camera is also likely being held at an unusual angle and position very close to the lens. Note how the pin appears to have different lengths in the last two pictures with just a small change in camera position.
• The ring the pin is sticking through is recessed. This makes the pin appear longer than it otherwise would.

It seems unlikely that not having a moving mirror would allow the Pellix to be able to take a longer pin. The mirror in FD mount lenses is above the aperture-control linkage. Whether a mirror is present or moves does not affect how long the pin can be.